On the evening of December 20, 1968, at the end of a tumultuous and frightening year for the United States, a new monster emerged from the dark.
The 60s had been an era of assassinations and political scandals, war and upheaval.
As the decade drew to a close, Americans had a sense that their social fabric was fraying at the seams, that such relentless violence would only beget more violence.
David Faraday and Betty Lou Jensen, two teens on a date, had no idea they were next.
The couple went to a Christmas concert together in their northern California town of Benicia before stopping their car on a secluded lover's lane for some privacy.
David had promised to have Betty back home with her parents by 11pm.
But moments after her curfew passed, a motorist driving down the secluded lane noticed something amiss with a station wagon parked in the shadows.
The passenger door was thrown open, and a few metres down the road was the body of a girl with five gunshot wounds to her back.
A male teen had also been shot and was barely alive after attempting to crawl away from the car. He died before an ambulance could get him to hospital.
For detectives, the crime didn't make a lot of sense.
There were no signs of robbery or sexual assault, and while police initially investigated the slayings as potentially drug-related, David and Betty were model students who didn't seem the type to be mixed up with gangs.
Counter-culture might have been flourishing in nearby San Francisco, but the towns that lined the surrounding bay were still sleepy, rural pockets of traditional Americana.
"There were no serial killers back then," Betty's school friend Sharon Henslin Stutsman told SF Weekly in 2018.
"All the detectives thought it had to be because of drugs. They refused to hear anything else."
The murders went unsolved for seven months — until the killer himself called up the police station in the neighbouring city of Vallejo to make two stunning confessions.
First, he announced that just 45 minutes prior, he had shot a young couple talking in their car in the parking lot of a nearby park.
Once again, the killer meted out more violence for his female victim, shooting 22-year-old Darlene Ferrin nine times. Michael Mageau was shot four times but survived the attempt on his life.
"I want to report a murder," the mystery man said to the dispatcher in a monotone voice.
"You will find kids in a brown car. They were shot with a nine-millimetre Luger. I also killed those kids last year. Goodbye."
On the phone was a man who called himself the Zodiac Killer.
His call would kickstart a game of cat-and-mouse with California police that lasted years.
At a time when serial killers seemed to be terrorising the country from coast to coast — Ted Bundy, Jeffrey Dahmer, Son of Sam, the Golden State Killer — one has always loomed larger in the American consciousness.
The Zodiac Killer was California's bogeyman, an attention-seeking megalomaniac wielding a shotgun and a knife, who seemingly chose his victims at random and then taunted the police and the local press with menacing phone calls and cryptograms.
To this day, he has never been found and the San Francisco Police Department still lists the murders as cold cases.
Decades after he rained terror over the San Francisco Bay Area, dedicated true crime sleuths continue to pore over the details of his murders, the letters he sent to news outlets and the puzzling codes that accompanied them.
But despite a mountain of evidence suggesting a serial killer was operating in plain sight, there has only ever been one named suspect, who died in 1992.
Fifty years on, it appears the mystery of the Zodiac will never be solved.
The Zodiac Killer sought publicity
Northern California was a hub of change and possibility in the late 1960s.
As harmony turned to division, Americans flocked to the San Francisco Bay Area in one of the largest migrations of young people in US history in search of counterculture, freedom and the summer of love.
But what started out as a quest for peace and free love would end in violence and a string of killings two years later when the area became a hunting ground for one of the country's most famous murderers.
The Zodiac wasn't just a killer. He was also a glory seeker who delighted in the attention of the press and in taunting the families of his victims.
As police searched for possible motives for the killings on December 20 and July 4, 1969, an unlikely clue arrived at California's largest newsrooms.
On August 1, three bulky envelopes were delivered to the offices of the San Francisco Chronicle, San Francisco Examiner and Vallejo Times with an instruction to "please rush to the editor".
Inside were identical cover letters accompanied by different cryptograms from a person claiming to have killed David Arthur Faraday and Betty Lou Jensen last Christmas, as well as Darlene Ferrin the month prior.
To prove his identity, the author listed some facts that "only I and the police know", including the brands of ammunition used in the murders, descriptions of the crime scene and the positions the bodies were found in.
It was confirmation that the two incidents were linked and that a serial killer might be behind it.
The anonymous writer demanded the publishers include the three cryptograms enclosed in the envelopes in their evening editions by the following Friday.
The codes were an odd pattern of capital letters, shapes and symbols set in neat rows.
The letter's author threatened to go on a murderous rampage if his demands weren't met and signed off the note with a signature consisting of a circle bisected by a cross.
All three newspapers published the codes and handed them to police, with the best code breakers in the business put to work attempting to crack the cipher.
But investigators were sceptical that the author of the notes was really the man they were searching for.
"We're not satisfied the letter was written by the murderer but it could have been," Police Chief Jack E Stiltz told the San Francisco Chronicle.
No-one could immediately unpick the lock set by the anonymous killer. (Decades later, dedicated sleuths are still trying to unravel some of the ciphers).
With the clock ticking on his Friday deadline, the writer sent a follow-up letter three days later, introducing himself as the "Zodiac" for the first time and providing more horrifying details about his crimes.
He also promised the code was the key to unravelling the mystery of his identity.
"When they do crack it, they will have me," he wrote.
The cryptogram was eventually solved by school teacher Donald Harden and his wife Betty, over breakfast.
It turned out to be a 408-symbol cipher, which the couple guessed by correctly assuming the writer would use the word "kill" in his note.
But instead of shedding light on the person behind the crimes, as the note had promised, the translated code only revealed the killer believed his victims would be his "slaves" in the afterlife.
"I will not give you my name because you will try to [slow] down or [stop] my [collection] of slaves for my afterlife," he wrote.
Police were back at square one.
The pattern of behaviour suggested the Zodiac was targeting students in and around their cars.
He also preferred to strike in the evening, and usually on weekends.
In lieu of a suspect and a reason for the killing spree, experts put forward various motives for the murders, including a Freudian theory that the Zodiac was striking out against those demonstrating an intimacy he craved.
More murders followed, accompanied by creepy phone call confessions, ominous letters and indecipherable cryptograms.
Despite the narcissism of his publicity-seeking, the delusion of his coded messages and the mountain of evidence piling up, police were no closer to finding the violent stranger stalking their streets.
The murder spree spiralled until it suddenly stopped
On September 27, 1969, college students Bryan Hartnell and Cecelia Shepard were enjoying a picnic in a secluded spot at Lake Berryessa Park, 30 kilometres north of Napa.
The weather was warm and sunny and the two old friends were catching up "for old time's sake" when they spotted a strange man lurking nearby.
Believing they were alone, they were struck by the stranger's appearance.
Dressed in a dark blue executioner's hood with slits for the eyes and mouth, the man wore clip-on sunglasses and a white crossed circle emblazoned on his chest.
In his hand, he brandished a gun.
He told Bryan and Cecelia he was an escaped prisoner and wanted their money and car keys so he could escape to Mexico, a claim that was later proved false.
Using 1.8-metre strips taken from a plastic clothesline, the stranger tied their hands behind their backs and between their legs, before stabbing Bryan 10 times with a 12-inch blade until he collapsed.
He then attacked Cecelia 24 times until she fainted, striking in a frenzy of laughter before creating the pattern of a cross on her torso.
A fisherman discovered the couple while passing by and alerted police, but they had already been tipped off by an anonymous caller using a payphone outside a car wash in Napa.
"I want to report a murder — no, a double murder. They are 2 miles north of park headquarters … and I'm the one that did it," the man said.
When they arrived on the scene, police discovered the familiar calling card of the Zodiac, a crossed circle, on Bryan's car door accompanied by the dates of his previous murders.
The attack on another young couple late in the evening and the violence against Cecelia in particular — she was stabbed more than a dozen times more than Bryan — also matched the behaviour of the Zodiac's other killings.
Cecelia died in hospital two days later, while Bryan survived his injuries.
"He seems to make sure the women are killed. Not that he didn't try to kill the men, there's no doubt of that, but he seems to be more forceful with the women than the men," Sheriff Captain Don Townsend told the LA Times in 1969.
But there were a few things that stood out about the Lake Berryessa Park attack that made it different to the serial killer's prior crimes.
The most obvious was that he had changed his modus operandi, shifting from shooting to using a knife against his victims.
The Zodiac had also left a message on the car door, something he hadn't done previously.
Police also found a potential lead in the muddy embankment nearby: a handful of size 11 footprints.
But just as police were working off the new information in their investigation, the serial killer struck again in a different manner.
On October 11, doctoral student Paul Stine was driving a taxi in downtown San Francisco when a man hailed his cab and directed him to Presidio Heights.
He was shot in the cheek at the intersection of Cherry and Washington before he completed the journey. His assailant took his wallet, keys and a piece of his white T-shirt to wipe down the car for prints.
But before he could get away, three teenagers who witnessed the shooting and robbery called the police.
When two nearby officers drove by minutes later, they observed a white man walking north but didn't pull him over because he didn't match the description they were given.
The passer-by would later reveal that he was the suspect they were looking for.
In a seven-page letter to the Chronicle, the Zodiac Killer claimed he killed the cab driver and had been pulled over by police shortly after the incident.
He also provided proof of his crime, mailing in a torn piece of Stine's shirt.
To the police, it was evidence that the Zodiac Killer, whoever he might be, was growing bolder.
The cases were getting more attention in the press and investigators were under mounting pressure to find a culprit.
Stations were flooded with hundreds of phone calls each day from people claiming to have information on the serial killer roaming around the Bay Area.
Some of the tip-offs were hoaxes, while many others were red herrings. But authorities were determined to investigate every possibility, desperate for any leads on the man who taunted them.
The increasing frequency of the crimes had alarmed investigators. Stine's death had occurred just two weeks after the attack at Lake Berryessa Park.
Within a year, the Zodiac Killer had amassed a body count of five and left two others seriously injured.
The unspoken question on everyone's minds was not if the killer would strike again, but when.
Residents were also left reeling from the location of the recent attack. Until the shooting of Stine, the Zodiac had largely focused on areas on the outer limits of San Francisco.
Now it appeared he was venturing deeper into the heart of the city.
Many feared they could be next on the serial killer's list, the random nature of the attacks suggesting anyone could be a target.
But the shooting of the cabbie was the last confirmed crime of the man who stalked the Bay Area.
After 12 months of escalating violence, the Zodiac Killer seemingly ceased killing.
For more than a year after his last attack, he continued to write letters and mail in cryptograms taunting police.
In one letter that was mailed to attorney Melvin Belli, the author asked for help and claimed he could not "remain in control for much longer".
It also contained a bloodstained piece of Paul Stine's shirt and prompted a plea from the attorney to the Zodiac asking for advice on how he could be of assistance.
In other letters, the Zodiac threatened to use a bomb to kill children, referenced other crimes in the area and encouraged people to wear "buttons" in his honour.
He would also often include a score of himself, which increased in number, against the San Francisco Police Department, which remained at zero.
Most disturbing of all was his claim to have killed 37 people in total, in letters sent up until 1974.
And then he vanished without a trace.
Only one suspect has ever been identified
In the decades since the Zodiac's murderous rampage, countless theories have been posited about the motive behind his crimes and his true identity.
As many as 2,500 people were believed to be suspects. Among them were a retired United States Army sergeant and a former member of a right-wing militant group that harassed communists.
One man, Gary Stewart, is convinced his biological father was the Zodiac and has written a book about finding evidence that Earl Van Best Jr was behind the killings.
In 2021, deceased American house painter Gary Francis Poste was also named by a group of former cops, forensic analysts and retired military investigators as being the Zodiac.
The cold-case investigators, dubbed the Case Breakers Team, said a paint-splattered watch bought at a military base found by police after one of the murders was one set of evidence that linked him to the crimes.
They also cited a heel print of the same style and shoe size found at three other crime scenes and links between Poste's name and coded messages sent to police by someone claiming to be the killer.
But sources told the San Francisco Chronicle that the "evidence" against Poste didn't appear to be conclusive. The San Francisco office of the FBI said the case remained open.
Despite all the many guesses over the years, only one man has officially been identified as a suspect: Arthur Leigh Allen.
In 1971, a friend of Allen's, Don Cheney, told the authorities that he made remarks about "shooting tyres on the school bus and picking the little darlings off as they come bouncing out of the bus".
The words had stood out to Cheney because they echoed similar statements the Zodiac made in his letters to newspapers.
Allen was a Navy veteran and former elementary school teacher who was fired from his job and subsequently arrested for child molestation.
After Cheney's statement to police, lead investigator and inspector David Toschi went to interview Allen and during their conversation, he noticed the former teacher was wearing a wristwatch with the brand name Zodiac and a crossed-over circle.
It struck Toschi at the time because it was the same symbol the Zodiac killer used to sign some of his letters.
The San Francisco Police Department also found suspicious items during a search of Allen's trailer, including hunting knives and a freezer filled with dead animals.
In the three-part Netflix documentary This Is the Zodiac Speaking, David and Connie Seawater recall that as children, Allen — who was close with their mother — took them to all the sites of the Zodiac murders.
David also claimed that Allen confessed to being the serial killer who hunted the San Francisco Bay Area before he died.
But Allen was never charged in connection with the Zodiac cases and he died in 1992.
Police inspector Kelly Carroll told the San Francisco Chronicle that DNA evidence had ruled out Allen as a likely suspect.
"Arthur Leigh Allen does not match the partial DNA fingerprint developed from bona fide Zodiac letters," he said.
The enduring mystery of who the Zodiac might be means there will always be more questions than answers.
"I've heard so many theories, they tend to all run together," San Francisco Police Lieutenant Tom Bruton told SF Gate in 2000.
"The 100th time you pick up the phone on one of these calls, it's just another wacko who is pulling something out of thin air."
Why the case remains a mystery
It's possible that the Zodiac's brush with the law after murdering the cab driver spooked him so thoroughly, he decided to slip back into society and never kill again.
Unlike other serial killers, who were propelled by a relentless need for violence, the Zodiac's ultimate goal seemed to be notoriety.
By retreating into the shadows, he continued to loom like a spectre over the Bay Area for the next five decades.
There he may remain forever.
Despite the wealth of communication he appears to have left behind, there are no confirmed samples of DNA from the Zodiac and only a vague police sketch of a man who could be anyone.
A partial DNA profile was found on a letter purportedly sent by the killer, but there's always a chance it was material left by a postal worker or someone else who handled the mail.
The size of the sample, derived from saliva off a licked stamp, is also not precise enough to pinpoint the Zodiac. Instead, it may only ever be used to rule out potential suspects.
And so, in ending his campaign of terror through California, the Zodiac got what he always wanted: infamy.
His crimes have inspired documentaries, a David Fincher film, a bottomless podcast playlist, an array of websites and forums and lots and lots of books.
"It's his ability to stay at large," James Alan Fox, professor of criminal justice at Boston's Northeastern University, said in 2007.
"Had he been caught, the whodunit would have been answered. Then you also have the bizarre elements of the case — the use of the Zodiac symbol, taunting the police.
"The publicity is often a fringe benefit to serial killers. They feel superior, unstoppable, uncatchable. They will play the game because they enjoy the celebrity they achieve."
But for the families of David Faraday, Betty Lou Jensen, Darlene Ferrin, Cecelia Shepard, and Paul Stine, there are only questions left unanswered.
"She was the oldest and my idol," Darlene Ferrin's sister Pam Huckaby said in 2019.
"She's been gone most of my life, and of course I miss her. Our parents died not knowing who killed their oldest daughter."
