All language subtitles for Cracking.The.Code.S01E02.720p.AMZN.WEB-DL.DDP2.0.H.264-Kitsune.[eng]

[dramatic music]

- [Narrator] Fear stalk the
streets of San Francisco.

[gun bangs]

- This guy is a
pathological, psycho killer.

- [Narrator] As the
death toll mounts,

the killer sends
out coded messages.

- It's like something
from a horror movie.

- [Narrator] He calls
himself the Zodiac,

but could cracking the
killer code reveal his name?

- He sets up this one
by saying, "My name is."

- [Narrator] But every
new code is more complex

than the last.

- The total number of
permutations would be bigger

than the number of
atoms in the universe.

- [Narrator] Now, 50 years on,
there's been a breakthrough.

- Kind of chilling.

Here were the words of the
Zodiac being heard again

for the first time
in half a century.

- [Narrator] These are the
codes that changed our world.

Bizarre markings, random
letters and numbers,

words that make no sense,

but cracking them
unlocks military secrets,

decodes ancient civilizations,

[gun banging]

and reveals enemies
in our midst.

[dramatic music intensifies]

Now we uncover how
they were decoded,

the genius minds
that broke them,

and the secrets they reveal.
[logo scraping]

[tense music]

San Francisco, Northern
California, 1968,

the week before Christmas,

the bodies of teenagers, David
Faraday and Betty Lou Jensen

are discovered on
a secluded lane

in the North Bay
area of the city.

[gun bangs]

David has been shot in the head.

[gun bangs]

Betty Lou has been shot
in the back five times.

- The boy was shot right
at the side of the car,

and the girl apparently
tried to run.

[Betty Lou yells]

And she was shot and
found 28 feet further on.

[gun bangs]

- From the very outset,

it was clear to the police that
they had a serious problem.

The first couple discovered
shot multiple times lying next

to their car in the most
innocuous of all places,

a make out spot.

[tense music continues]

- One of the first
assumptions is robbery.

You know, just
somebody pulling up

and robbing these two people
and somehow it went south

and killed them both,
but nothing was taken.

- The whole community was in
uproar. It was out of the blue.

No one knew what
happened or why.

- - [Narrator] Despite
media coverage,

detailed forensic work
and intensive interviews

with a couple's family,
friends and acquaintances,

the police fail to
make any arrests.

- One of the first
questions the police ask

whenever they come
across a murder

is what is the motive?

The vast majority of murders
are committed by people

who knew the victim, a
friend, a business associate,

a family member.

So they're gonna look for
some connection to the killer,

but there seems to
be no apparent motive
for the killings.

- [Narrator] With no leads,
the trail quickly goes cold,

[eerie music]

then less than seven months
later, there's another shooting,

just a few miles from
the first crime scene.

The victims are
22-year-old Darlene Ferrin

and 19-year-old Mike Mageau.

The MO is disturbingly familiar.

- You have a couple parked
in a secluded location,

approached and brutally
assaulted, again,

with no apparent motive.

- The car pulls up behind them.

A lone guy gets out, opens fire.

[guns banging]

He got back in his car
and then drove away.

- [Narrator] 40 Minutes
after the shootings,

the nearby Vallejo
Police Department

receives an anonymous call.

- The caller has detailed
information about the crime.

He's able to describe the
location, the color of the car,

and even the weapon
used in the murder.

A nine-millimeter handgun.

- [Narrator] These are details
only the killer could know.

- Police are now thinking,
"How do you know this?

You must have been there. It
can't just be a prank call.

This can't be a coincidence."

- [Narrator] And the caller

makes a second
chilling confession.

- He claims responsibility

for the killings
seven months earlier,

but before the police can
trace the call, he hangs up.

It's clear to them, though,
that the same man is responsible

for these crimes.

[dramatic music]

- [Narrator] As news of a
second double shooting spreads

across the North Bay area,

local journalist Duffy Jennings
senses the panic spreading.

- The fear and the
tension started to build

because of the media exposure.

- [Narrator] The one difference

between the killers
first and second attacks

is that this time
there's a survivor,

[gentle dramatic music]

but 19-year-old Mike
Mageau is so traumatized,

the police still
have little to go on.

- The description is so vague.

It really doesn't leave
the police with any clues

that they can
follow successfully.

- He's had such a traumatic
experience that the things

that he'll remember from that
moment will blur into one.

He was shot. He
was left for dead.

[dramatic music]

- [Narrator] Two brutal
attacks, seven months apart.

And there's still little
progress in finding the killer.

- We don't know who he is. We
don't know why he is doing it.

We don't know where he is
gonna shoot somebody next.

It was a real mystery.

- [Narrator] The trail for
the serial killer goes cold.

[upbeat music]

Then eight months after
the killing spree began,

there's an astonishing twist.

Someone claiming to be the
killer sends handwritten letters

to three local newspapers.

- This is a really unprecedented
set of circumstances.

A killer that is
openly communicating

about the crimes
they've committed.

- [Narrator] The letters
contain unpublished details

that only the police and
the murderer could know.

[suspenseful music]

And each letter carries
the same strange sign off.

- When the killer
wrote to the newspaper,

signing off with this symbol,

which was a circle
with cross lines in it,

everyone immediately took
that to mean the crosshairs

of a rifle scope.

- [Narrator] The killer sends
more than just the letters.

Each of the newspapers also
receives a sheet of paper

covered in strange combinations
of letters and symbols.

- There were circles, circles
with lines through them,

triangles and everything

had this crude,
handwritten quality.

[dramatic music]

- [Narrator] It is
the killer's personal

and very deadly code,

containing more than
400 letters and symbols.

- Police are not
trained in espionage.

This is not their
area of expertise.

So when they receive this code,

it's just outta their league.

- [Narrator] To focus
police attention

on his mysterious code,
the killer promises

that cracking it will
reveal his identity.

- Police work is based on
the specific methodology,

forensics and looking
at the crime scene

and speaking with witnesses.

And now they're getting

this mysterious code directly
from the killer themselves.

They just don't know
what to do with it.

[siren blares]

- [Narrator] The
police reach out

to the FBI's top cryptologists,

but cracking the strange code

isn't the investigators'
only problem

because the killer's letter
also contains a threat.

"Print a section of the
code on the front covers

of the three national newspapers

or the body count
will keep rising."

- The newspapers are the
thing that everybody reads,

that everybody will see.

You're gonna get it
out to a lot of people

to make sure that
you are noticed.

He's letting people
know that he's here.

- [Narrator] In a bid to
prevent any more deaths,

the decision is made to concede
to the killer's demands.

The coded messages
are published,

but the police
publicly cast doubt

on the messages' authenticity

and request more from
the letter writer

to prove he's the killer.

- On the surface they're saying,

"Prove that you're
telling the truth,

prove you are who
you say you are,"

but really they're just trying

to get the information
necessary to catch the guy.

- They need him
to fall over a bit

so that they can
catch up with him.

[dramatic music]

- [Narrator] The plan
to goad the killer

into responding, pays off.

He sends another letter.

This time, his opening
line is haunting.

- [Zodiac] Dear Editor.
This is the Zodiac speaking.

- For the first time,

he identifies himself
as the Zodiac Killer.

And that's how he'll be
known from here on out.

- The Zodiac Killer is now
forcing his own narrative.

He's taking control
of his new persona

and his new personality.

He is the Zodiac, he's here
and he's building his brand.

- And by giving himself a
title, he's handed the press,

journalistic gold,
they have a villain

that they can write
stories about,

and that name will soon
become a household name.

And you have to think
that with all his actions,

this is exactly what the
Zodiac Killer hoped for.

- First of all, he's saying,

"I'm smarter than anybody else."

And second, it became kind
of a game to him while people

are lying dead
and their families

are mourning their
dead relatives.

This guy's getting a kick
out of whatever he's sending.

[eerie music]

- [Narrator] Once again,
the letter contains details

only the killer could know,
and he taunts the authorities

for their failure
to crack his code.

- He doesn't really think
they're going to break the code.

And he's just gonna sort of
tease them a bit about it.

Again, trying to assert that
he's the superior person here,

that he's really running
the show, not the police.

- He's really enjoying
this cat and mouse game.

He's sending out
something, the mystery,

the legacy that he's leaving.

He's really enjoying
making people confused

and making people think
and making people fearful.

That is exciting to him.

- [Narrator] The
Zodiac's latest letter

doesn't bring the
police any closer

to working out his identity,

[mysterious music]

but making the code public
has an unintended benefit.

The police and FBI
cryptographers are joined

by hundreds of amateur code
breakers across America,

all searching for ways to break
the Zodiac's cryptic code.

- Zodiac Killer uses
a cipher that seems

to be replacing each letter
with some kind of secret symbol.

And these are symbols that
apparently he's invented.

The first step in decoding it

is just to figure out
what type of cipher it is.

- [Narrator] The patterns of
symbols lead many code breakers

to suspect the Zodiac
is using a variant

of a code dating back
to the first century BC,

[tense music]

a substitution cipher.

[lively dramatic music]

Substitution ciphers were used

by one of the most famous
Roman leaders of all time.

- Turns out that Julius Caesar

was quite a keen cryptographer.

Caesar would shift every
letter up three places.

So a becomes D, B becomes
E, C becomes F, and so on.

And that is the
classic Caesar cipher,

shifting every letter
up three places.

But nowadays, when we
talk about a Caesar cipher

we're we're just saying
shift up letters,

any number of places.

[dramatic music]

- [Narrator] The key to cracking

this basic substitution cipher

is knowing this shift pattern.

In its most basic form, the
Caesar cipher is limited

to the number of other
letters in the alphabet

other than itself, giving
25 different possibilities.

- The problem with a classic
simple substitution cipher

is that you can break it
with frequency analysis.

So by that, I mean, some letters

are more common than others.

- [Narrator] In English,
the letter A accounts

for 8% of all letters in
a typical page of text.

E accounts for 11%. T
appears 7% of the time.

And Q just 0.1%.

That means if all
letters are substituted

by just a single symbol,

working out the percentage
they appear within a text

will reveal which letter
each symbol represents.

- And soon or later,
probably sooner,

we'll find out what
the message says.

[eerie music]

- [Narrator] The
FBI cryptologists

and the amateur code
breakers suspect

the Zodiac is using a
substitution cipher.

But despite that, this code is
stubbornly difficult to crack

because the Zodiac has
added a complex twist

to his coding method.

- It's immediately
clear that this

is not a one-to-one substitution
of the English alphabet

because in the English alphabet,
there are only 26 letters.

- Even if you add in the
numbers from zero to nine,

the numerals, it's
still not enough.

There's something else going on.

- [Narrator] There are more
than twice the number of symbols

in the Zodiac's code than there
are letters in the alphabet.

Cryptologists suspect
he's using more

than one symbol to
represent the same letter.

- For example, for the A you
might have the number one

or B the letter M
or another symbols.

So you have several
symbols to choose from.

- [Narrator] And that means
frequency analysis on its own

isn't enough to break
the Zodiac's code.

- Because there's nothing
that's standing out

because there's no obvious
variations of frequencies,

it's very hard to then begin
to decipher that message.

[upbeat music]

- [Narrator] As efforts to crack
the Zodiac's code continue,

the unknown killer
remains at large,

the feeling of terror across
San Francisco intensifies.

- So releasing this
code to the public,

it's a bit of a
double-edged sword.

On one hand, you're enlisting
this vast knowledge base

to help you solve this mystery.

But at the other hand,
you're giving something

that's already received
press even more press,

and you run the risk of
greatly exacerbating the fear

that the general
population already

is suffering from
about this guy.

- [Narrator] Two weeks after
the Zodiac's coded message

is published, parts
of the city feel

like they're
verging on hysteria.

The police are at a total loss.

[siren blares]

[gentle eerie music]

Then a breakthrough
comes from left field,

two crossword
puzzle enthusiasts,

get in touch with the police.

- Some of the greatest code
breakers have been people

who also love crossword
puzzles and word games

and number games because
you have to have a mind

that's able to focus
on the details,

but also think about
kind of crazy intuitive,

out-of-the-box possibilities.

- [Narrator] Teacher Donald
Harden and his wife Bettye

claimed to have done
what the best minds

in the FBI couldn't,

they say they've cracked
the killer's code.

- Bettye and Donald
Harden became intrigued

by the Zodiac puzzle, like
thousands of other people.

And almost as if they
were sitting down

to solve a Sunday crossword
puzzle, they went to work on it,

but they worked on it
with a really smart plan.

They knew they had to find
some set of characters

they could connect
to a real word,

something that frequently
repeats in the document.

This is a classic technique
for code breaking.

You look for what's
called a crib,

some combination that
keeps popping up.

- [Narrator] The Hardens
have used exactly

the same techniques created
more than three decades earlier

by some of the greatest
code breakers in history.

[dramatic music]
[boots clicking]

During World War II,
the German Army relied

on a secret code to pass
messages onto Nazi forces,

generated by their now
legendary Enigma machines.

The encrypted messages were
thought to be impenetrable.

- The Enigma code is
a substitution cipher.

You swap one letter
for a different letter,

but the difference with the
Enigma cipher is its dynamic.

The same letter
is being encrypted

by a different
letter differently,

each time you hit the key.

- [Narrator] The Enigma
machine's dynamic encryptions

made British code breaking
efforts almost impossible.

- There are millions
upon millions of
different permutations

that are going on here.

And unless you know the
millions upon millions

of permutations,
you've got no idea

what this code really means.

There's no way of going back
to the original message.

- [Narrator] The Germans made
cracking Enigma even harder

by changing its
settings every 24 hours.

- It would've taken an
army of analysts decades

to crack the code.

[dramatic melodic music]

- [Narrator] British
code breaking efforts

were only saved by the discovery

of a critical design
flaw in Enigma.

It couldn't code a
letter as itself.

- If I type the letter
A into an Enigma machine

a lamp board lights up
with another letter,

that letter will never
be A, if I type B,

B will never light up,
C, C will never light up.

It narrows down all
the possibilities.

- [Narrator] It was a
critical breakthrough

for British code breakers.

They just needed to find a way
to exploit their discovery.

- So they look for
things called cribs,

which are essentially
repeating words.

So this might be, Heil Hitler,

which was used
frequently as a sign-off.

- If we can match one word

that you've guessed
in the message

with a bit of the
encrypted message,

then you can begin to pin down
the settings of the machine.

- [Narrator] Enigma settings
were changed at midnight.

So to give them as
much time as possible,

the British code
breakers hunted for cribs

to Enigma's daily codes

in one of the most mundane,
early morning transmissions,

a weather report sent
out at 6:00 am every day.

- So a weather report
was particularly useful

because it would be
a daily transmission

that they would make,
it was fairly routine.

So any repeating pattern
like that was vital.

- [Narrator] British
code breakers

searched the early morning
code for strings of characters

that could disguise the words
for weather report in German.

- So let's imagine I've
intercepted a message

from weather station.

And I think it's got
the word wetter in it,

W-E-T-T-E-R, the German
word for weather.

It must be in there somewhere.

It's a weather station report.

Well, is it at the beginning
of the message? W-E-T-T-E-R?

Well, no, because the first
letter of the encrypted text

is a W and I know no letter
can be encrypted as itself.

So I shift the wetter
along a little bit

until I find the
word wetter encrypted

with six completely
different letters.

Now that doesn't mean that's
the right place for wetter,

but it tells me that it's
potentially the right place.

- So if they identified a
word that was repeating,

such as weather report,

that would give them all of
those individual letters,

which was a massive
key to then unlock

the rest of the day's coding.

It was a huge advantage.

- [Narrator] Weather report
was the first of many cribs

that British code breakers
correctly deduced,

all these cribs were
key to cracking Enigma.

It provided British
intelligence with some

of the German military's
most closely guarded secrets.

- Once you know how
these messages work,

it's very easy to guess the
cribs and you are cracking them

more and more quickly
as the war progresses.

- All of this information
was absolutely vital

to the Allied war effort.

People now looking back say,

"Perhaps it shortened the
war by even up to two years."

[bomb explodes]
[suspenseful music]

- [Narrator] 30 Years later,

crossword enthusiasts Donald
Harden and his wife Bettye

apply the same crib hunting
technique to try to crack

the Zodiac Killer's code.

- So the Hardens thought,
"Well, this guy's a killer.

He's bragging about his killing.

What are some of the words he
might be using in a document?"

- [Narrator] The Hardens
begin their search

by looking for
patterns in the symbols

that could represent a
very obvious word choice

for a serial murderer, kill.

[dramatic music]

And slowly the Zodiac code
finally begins to crack.

The first step is
spotting a character

that appears more than once,
like the half filled squares.

- They spot some
symbols that repeated.

So that could be the
double L in kill.

- [Narrator] If these
represent double L,

then the diagonal line could
be a K and the triangle

could be an I,
completing the word kill.

- The eye is really useful

because it's the first
letter of the message.

And as part of the
guesswork of figuring out

what this killer
is trying to say,

it really stands to
reason that I would be

the first word of the message.

- [Narrator] The symbol
the Hardens believe

is the letter I match
and a possible first line

begins to emerge.

- The first line of the
Zodiac killer's message

was the key for the solution

of the how the two
broke into the cipher.

- [Narrator] But the killer
has used far more symbols

than there are letters
in the alphabet.

So the Hardens know each letter

has more than one substitution,

just like solving a crossword,

they use a mixture of logic
and educated guesswork,

until every word in the
first line is revealed,

and eventually,
the entire message.

[dramatic music continues]

A pair of crossword-loving
amateurs has
succeeded where some

of the country's most elite
code breakers have failed.

The message confirms just
how twisted the Zodiac is.

- The deciphering starts,

"I like killing people
because it's so much fun.

It's more fun than killing
wild game in the forest

because man is the most
dangerous animal of all."

- When the decrypted
message was released,

it had probably exactly the
result the Zodiac Killer wanted.

It just horrified people,

someone who was taking
this perverse pleasure

in not only killing people,

but then bragging
about it to the public.

- [Narrator] Despite the
killer's promise in his letter,

the message the Hardens
reveal does not identify him.

The police are
back to square one.

- When they do crack
this first code,

all they really learn
is that the killer

is taking great
pleasure from his acts

and that he's not going
to stop anytime soon.

[dramatic music]

- [Narrator] The Zodiac is
toying with the authorities

and they know it.

The police are no closer
to identifying him

than they were the
first time he killed.

This does nothing to
calm the fear rippling

across the Bay Area
of San Francisco.

- There is a killer on the
loose, he enjoys killing.

He strikes seemingly at
random and without warning

and the police have
no idea who he is.

- "Is he coming for me?
Am I gonna be targeted?

What does he want?"

I don't understand all of
this will be going through

the community's his mind.

- It's horrifying to
think that this person

could be out there
walking among us,

looking for the next opportunity

to play this really sick game.

[dramatic music continues]
[siren blares]

- [Narrator] With the police
no closer to catching him,

the killer is about
to ramp up the fear

already infecting San Francisco.

[eerie music]

September 27th, 1969,

less than three months after
the second Zodiac killings,

[phone rings]

the Napa County Sheriff's
Office receives a phone call.

It is from the Zodiac Killer.

He has struck again,

and he wants to be sure
the police know it was him.

- The caller at the time
couldn't know that the police

had already been tipped
off by a local fisherman.

So they were on the scene.

They were already
investigating the crime,

when this call comes in.

- [Narrator] At Lake Berryessa,
north of San Francisco,

college students Bryan
Hartnell and Cecelia Shepard

have been stabbed multiple
times and left for dead.

The latest attack carries
many of the hallmarks

of the Zodiac, and this time,

the attacker has left
behind a calling card.

[creepy music]

- There is the message left on
the side of the victim's door

with the dates of the Solano
County murders and ours,

along with other items
that are on there,

have definitely indicated to us

that they're one and the same.

- This is a killer that is going

to spend time
setting up a scene.

He's communicating a message

to whoever's going to
discover his victims.

- [Reporter] Police and park
rangers combed the scene

for clues until late yesterday,

it was here the
couple was picnicking.

And here a man in a mask robbed,

tied and stabbed them,
leaving them for dead.

- [Narrator] The Zodiac

has now attacked
six innocent people,

but once again, the
killer has slipped up.

When the police reached the
scene at Lake Berryessa,

both victims are still alive.

- [Reporter] Sergeant Bill
White was first on the scene.

- The guy had told him,
he said, "Take the money."

He said, "I don't want it.

All I want is to kill you
people, I have to kill you."

Well, he started stabbing
the kid in the back.

Real nice college kids, just
stabbed for no reason at all.

I never witnessed
anything like it before.

- So Cecelia is able
to give some clues

as to the appearance
of the Zodiac Killer,

but her wounds prove fatal
and she doesn't survive.

So the Zodiac Killer
has attacked six people,

four of them have been killed,

and still the police, beyond
this vague description,

have no idea who
they're dealing with.

- [Narrator] Any hopes
for a detailed description

of the Zodiac Killer, now
lie with Bryan Hartnell.

He has been stabbed six
times, but miraculously,

none of his injuries
are life threatening.

For the first time,

police have a full
description of the attacker.

- Can you describe for us what
your attacker looked like?

- He was a medium
to short height.

He had this black hood on,
came clear down to here,

just little slits in the eyes

and wears these clip-on glasses.

- [Narrator] An artist's
impression of the Zodiac

based on Bryan
Hartnell's description

is released to the public.

[suspenseful music]

- Finally, terror has
an image to go with it.

- [Narrator] But because
the executioner-style hood

completely obscured
the killer's face,

it doesn't move the police hunt.

[siren blaring]

On there is still a
killer on the loose.

And no one is certain
what he looks like

or where he will strike next.

- This guy is a
pathological, psycho killer.

There's no doubt about it.

- Day to day, you weren't
sure where the next

random violent attack
was gonna come from.

[tense music]

- [Narrator] Just two
weeks after the stabbings

at the lakeside, the Zodiac
Killer ups the stakes again,

All his previous victims have
been found in remote spots

on the city's outskirts,

but the killer is clearly
growing in confidence

or at least in his
thirst for publicity.

[gentle dramatic music]

When taxi driver Paul Stine
is discovered shot dead

in his car in Presidio Heights,

a busy neighborhood
of San Francisco,

it is such a different
MO the police

don't immediately connect
it to the Zodiac Killer.

- So when they got there
and found the driver

with a bullet in his head,
blood all over the place,

that assumption was
that it was a robbery.

And so they just conducted it

as a regular homicide
investigation.

[lively dramatic music]

- [Narrator] That all
changes when the newsroom

of the "San Francisco
Chronicle" receives a package

containing a piece of Paul
Stine's blood-soaked shirt.

Packed in with the
shirt is a third letter

with the now disturbingly
familiar symbol at the end.

- It was the first and only
known time that he struck

in the city of San Francisco.

And it broke his MO of
attacking young couples

in lover's lane or
picnic situations

as he had done three
times prior to that.

So now all bets are off.

- [Narrator] The Zodiac's
latest letter suggests there

are now no lengths
he will not go to,

to increase his notoriety.

The letter says, he's come up

with a whole new kind
of killing spree.

This time, it will be children
leaving their school bus.

[eerie music]

- With the letters
threatening more killings,

threatening to shoot kids
coming out of a school bus,

now the entire region is
gripped in this fear of

the unknown potential killer.
[siren blares]

- Police respond
extraordinarily.

They put out extra patrol cars.

They assign police to
monitor the school buses.

- [Reporter] The bus
patrols started first

in this county Wednesday.

Police units from various
agencies using marked

and unmarked cars, follow
buses on their runs

to and from schools.

- They're trying to
do everything possible

to prevent the attack that the
Zodiac Killer has threatened.

- [Reporter] The massive
patrols are responses

to the Zodiac Killer's
threat to stop a bus

and shoot children.

- [Narrator] Local beat
cops work up a picture

of a man seen near
the Stine killing.

Could this be the face
of the Zodiac Killer?

If it is, it still
produces no leads.

For 10 months, the Zodiac Killer

has terrorized the
San Francisco area.

He has brutally
slain five people,

and seriously wounded two more.

Although the killings and
threats have continued,

one thing has stopped

since his first
elaborate Caesar cipher,

cracked by two crossword buffs,

there have been
no further codes,

[dramatic music]

but three weeks after the murder
of taxi driver Paul Stine,

a new code is delivered to
the "San Francisco Chronicle."

And this one is far more complex

than the Zodiac's first attempt.

- The killer realized
that his first message

was broken pretty soon.

So he added another step of
complexity to the second one.

He probably still
wanted it to be solved,

but he wanted to make it harder.

- [Narrator] The
Zodiac's new cipher

contains 63 different symbols.

Nine more than is first.

And the message is 80
characters shorter.

These two changes make
cracking this code,

a monumental challenge.

- The shorter the
message, the fewer words

are gonna be repeated.

The fewer opportunities
you have to check

what might be a
common substitution.

- So it's clear at
this point that whoever

is conducting these killings
is an intelligent individual,

that he has some
type of plan in mind.

And now, he's raised
the complexity of things

with his new code.

- You get the sense
that he was taking

this perverse
pleasure in this game.

- [Narrator] Amateur and
professional cryptologists work

around the clock to try to crack

the Zodiac's latest message.

Over the next five months,

the killer sends a further
two letters to the newspapers,

mocking the police further
for their failure to catch him

or crack his latest code.

- It's almost as if he got
more of a kick out of hiding

in plain sight, if you will,

almost than the actual
murders themselves.

[soft dramatic music]

- [Narrator] 14 Months

after the Zodiac's
killing spree began,

the police still have five
unsolved murders on their hands.

They don't have a single lead.

Then in April, 1970, the
Zodiac releases a third code.

- This is spurring his ego.

"Look how intelligent I
am. Look how great I am.

I'm gonna give you something

that you are never
gonna figure out."

- [Narrator] The latest code
contains just 13 characters

and the Zodiac promises
that cracking it

will finally reveal
his identity,

but no one can crack it
because that's impossible.

- This one, he sets up
by saying, "My name is,"

and then he delivers
13 characters,

13 symbols that
made it essentially
impossible to decrypt,

if it wasn't closely related
to one of his previous ciphers.

- If the message as
short as it is here,

it's not possible to check if
your assumption is correct.

- [Narrator] The whole
third code is nothing more

than yet another opportunity

to taunt the police
for their failure.

- Hundreds of people sat
down to try to break it

and came up with plausible
sounding explanations,

but pretty much any 13 letter
word might be plausible.

There was no way to
prove or disprove,

even the likelihood
that one explanation

was better than another.

- [Narrator]
Something is changing

in the Zodiac Killer's approach.

Killing seems to be
taking a backseat

to increasingly bizarre demands

for publicity, and increase
in threatening letters.

a diagram of a homemade bomb,

he warns he's going
to plant somewhere.

He even demands that the
public starts wearing buttons,

carrying his notorious
signature symbol.

- These are thoughts
of a delusional person.

His narcissism's gone to
a different level here.

"I am now impatient.

You need to do what
I'm telling you to do.

Why haven't you seen how great

and powerful I am before now?"

- [Narrator] When the demand

that people wear
his symbol fails,

the Zodiac sends a
fourth code and a map.

He claims that combining the
map with a 32-character cipher

will reveal the
location of a bomb.

[tense music]

- So the police have this map,

but they need to break this
code, if they're going to get,

what seems to be a vital
piece of information,

the coordinates where
the bomb is hidden

and hopefully save some lives.

- [Narrator] He's no longer
boasting about his achievements.

Instead, he's sending a warning,

a warning with just
one purpose, fear.

- He's now changed his tactic

and he's doing it to
try and build that fear.

He wants the recognition
from further afield

and what's more recognizable?

Well, an act terrorism.

- [Narrator] But if
the bombs coordinates

really are hidden within
the 32-character cipher,

code breakers fail
to reveal them,

no explosion is ever reported.

It is the last code
the Zodiac ever sends.

[tense music continues]

The letters, however,
do keep coming.

Between 1970 and 1974,

up to 10 more are sent
to the police and press.

And each time the
tally of victims

the Zodiac claims to
have killed increases.

- As far as we know, Paul
Stine is the last victim,

but another letter is received
in which the Zodiac claims

to be responsible
for 37 other deaths.

It's an extraordinary
claim. Very hard to back up.

[mysterious music]

- [Narrator] In 1974, the
taunting letters suddenly stop,

the Zodiac Killer
disappears without a trace,

leaving just one last mystery.

Who was the Zodiac Killer?

The police never
closed the case.

For decades, the last three
codes that could reveal

the Zodiac's true identity,
remain un-cracked.

Until 2020, half a
century after the killer

sent out his second and
most complex cipher.

When a team of
amateur code breakers

spread across three continents

attacks the second Zodiac cipher

with cutting-edge software.

- They had tools
at their disposal

that just didn't exist in 1970.

By 2020, there was no question

that computers could easily
handle running thousands

and thousands of
tests of different
possible substitutions.

- [Narrator] The team suspects

that after creating his
substitution cipher,

the Zodiac may have
mixed up the symbols

using a pattern
known only to him.

If that was the case,

then before they can even
start on his original cipher,

they have to
unscramble the symbols.

- If a message in some kind of
cipher has been manipulated,

jumbled up in a way that
rearranges all the letters,

first, you have to
solve that layer.

You have to get back to what
the original cipher was.

And then you can go to work
trying to break that cipher.

[dramatic music]

- [Narrator] The team
tests this theory

by using the message he
sent as a starting point,

and trying to work backwards

to reconstruct the
killer's original cipher,

hackers call this
reverse engineering.

- It's very difficult
to decrypt a message

when you don't even know which
direction it's written in.

So what they were
trying to do essentially

is reverse engineer
whatever kind of grid

or algorithm the
Zodiac was using

in creating this cipher.

- [Narrator] The
team's computer program

generates 650,000 possible
versions of the encrypted text.

Any one of them

could be the Zodiac's
original ciphered message.

- So there was no guarantee
that this would work, right?

It could be that the
right permutation
was not in their list

because the total number of
permutations would be bigger

than the number of
atoms in the universe.

- [Narrator] The code breakers
run all 650,000 versions

through a decryption
program they have created.

Its sole purpose is
cracking the Zodiac code.

- In the scramble message,
nothing's repeated,

it's all random, but if
you can get the randomness

out of it, now you
can start looking

for those telltale
repeats of certain groups

of characters that could
stand in for certain words.

- [Narrator] For weeks,
the decryption program

produces streams
of garbled text.

Then on December 3rd, 2020
many months into the project,

they make a breakthrough.

- On one of their many versions
of the de-scrambled message.

They started seeing
some recognizable words.

They saw the phrase
"I hope you are."

And then elsewhere on the
page, "trying to catch me."

- [Narrator] Painstaking
analysis reveals

the successfully
decrypted words were read

in a diagonal direction,
starting in the
upper left corner

and moving across two places
for every subsequent line.

- Now they had strong clues

about how the original
message was scrambled,

in effect they'd reverse
engineered the Zodiac's system.

- So once you know the pattern

for how to reorder the symbols

and you think you've got a
lot of the words correct,

you can lock in those words
and look for substitutions

for the remaining letters to try

to crack the rest of the cipher.

- [Narrator] The team modifies
the decryption software

and runs it again.

And after more than 50 years,

the Zodiac's second
code begins to break.

- After going
through this process,

the team was faced with an
almost complete paragraph.

- The first line reads,

"I hope you are having lots
of fun in trying to catch me."

This was a real breakthrough
and also kind of chilling,

here were the words of the
Zodiac being heard again

for the first time
in half a century.

- [Narrator] Mirroring events
of more than 50 years ago,

it's amateur code
breakers who finally break

into a Zodiac code.

[dramatic music]

Many were hoping that
breaking the second code

would finally nail the
identity of the man

who terrorized San Francisco
half a century ago.

[tense music]

It doesn't, which is no surprise

to those who've studied him.

- This code is repeating the
same lines, the same things,

how he enjoys killing.

He doesn't mind dying,

but this doesn't
necessarily mean

this is what he's thinking.

This is bravado.

The Zodiac is constantly
putting out there

that he's going
to reveal himself.

He's gonna tell the police
what they want to know.

He's going to come
out, but why would he?

The ciphers, the codes that's
what's keeping him alive.

If he was a real person, then
that would all disappear.

We wouldn't have this
like legacy in this myth

that surrounds him.

So he was never going
to give anything away.

- [Narrator] The true identity

of the Zodiac Killer
remains unknown.

- We still don't know who
Zodiac is or was, if he's alive,

if not, if he is, where is he?

That's what keeps
this story going,

is the questions that
don't get answered.

[eerie music]

- [Narrator] Two of the
Zodiac codes remain unbroken

and it's possible
they do contain clues

that will one day
reveal the identity

of one of history's most
notorious serial killers,

but based on the
contents of the messages

that have been decrypted so
far, that seems unlikely.

- We're still left
with the question,

whether his name is really
in that code at all,

or is it just another hurdle

for the authorities
to jump over?

- I'm sitting here
50 plus years later,

still trying to
answer the question.

I think this will just
be one of those cases

that we probably
will never know.

- Would cracking
all of his codes,

give us the final
pieces of the puzzle?

Would we know the full
extent of his crimes?

And would we understand
the mind of that killer?

Perhaps, but that requires
us to crack those codes.

- The fact that there are
still these un-cracked codes

out there means
people will continue

to obsess over the Zodiac,

try to break these codes,
try to figure out who he was,

which in kind of a chilling
way is probably exactly what

the Zodiac Killer intended.

[dramatic music]
[computer beeping]

[adventurous music]

[bright upbeat music]