“I like killing people because it’s so much fun.”

In July of 1969, a letter arrived at The San Francisco Examiner newspaper containing those chilling words in a coded message. The sender: the soon-to-be-notorious Zodiac, a serial killer who terrorized Northern California in the late 1960s and early 1970s with a combination of grisly murders and bizarre public letters brimming with horrific threats, demented demands and mysterious ciphers teasing his identity.

That identity has stymied law-enforcement officials, professional code breakers and armchair criminologists alike for nearly five decades. While officially connected to five murders and two attempted murders, the Zodiac hinted he had killed at least 37 victims. After taunting the police and the public with nearly two dozen communiqués, he seemed to vanish in the late 1970s. But his twisted legacy endures, having inspired three real-life copycat killers and dozens of books, TV shows and movies—including, most famously, Clint Eastwood’s nemesis in the film “Dirty Harry.”

Below, a chronology of murders linked to the Zodiac and several that show signs of the Zodiac hand:

Robert Domingos and his fiancé Linda Edwards were seniors at Lompoc High School in Santa Barbara County in Southern California. On Tuesday in early June 1963, the couple decided to use the “Senior Ditch Day” to go sunbathing on a beach near Gaviota State Park. When the two teenagers didn’t return home by Wednesday, Robert’s father went to the beach and was horrified to discover their bodies lying together inside the remains of a crumbling shack. The victims, bound with rope, had apparently tried to escape but were shot and killed with a .22- caliber weapon. Robert was shot 11 times and Linda had been shot nine times. The killer then dragged the bodies to the shack where he tried and failed to start a fire. Investigators had few leads but, in 1972, the Santa Barbara County Sheriff’s Department announced a possible Zodiac connection. The beach killer used Winchester Western Super X ammunition, the same ammunition used by the Zodiac during the 1968 murders on Lake Herman Road. The Domingos/Edwards case also had similarities to the Zodiac’s attack of another young couple at Lake Berryessa in 1969.

Eighteen-year-old Cheri Josephine Bates lived with her father Joseph and was a student at Riverside City College in Riverside, California. On October 30, 1966, she left a note that read, “Dad— – went to the RCC library.” The next morning, her Volkswagen Beetle was found abandoned in the library parking lot, and her body was lying nearby between two houses. She had been stabbed several times and her throat was slashed. Police found a men’s Timex watch at the crime scene, a print from a military boot and some hairs in dried blood on the victim’s hand. Cheri Jo’s purse was intact, and an autopsy revealed no evidence of sexual assault. One month after the murder, the local newspaper and the police department received typewritten letters titled “The Confession” from someone who claimed to be the killer. The author wrote, “Miss Bates was stupid. She went to the slaughter like a lamb,” and added, “I am not sick. I am insane.” In April 1967, the newspaper, the police and Joseph Bates received virtually identical handwritten letters which read, “Bates had to die. There will be more.” The notes were signed with a symbol that resembled the letter “Z.”

In 1969, Riverside police contacted investigators in Northern California regarding the similarities between the Zodiac crimes and the murder of Cheri Jo Bates. Sherwood Morrill, then documents examiner for the California Department of Justice, concluded that the Zodiac was responsible for the notes linked to the Bates case. The “Riverside connection” was later revealed to the public by Paul Avery, reporter for The San Francisco Chronicle. Zodiac then sent a letter to The Los Angeles Times indicating that the killer confirmed the theory that he had killed Bates. The Zodiac wrote, “I do have to give them credit for stumbling across my riverside activity, but they are only finding the easy ones, there are a hell of a lot more down there.” Years later, Riverside police rejected the Zodiac theory and focused on a man who they said was a jilted former lover of Bates. In the late 1990s, police obtained a sample of the suspect’s DNA to compare with the DNA taken from the hairs found in the victim’s hand in 1966. The DNA didn’t match, and the suspect denied any involvement in the murder.

Five nights before Christmas, high school students Betty Lou Jensen and David Faraday set out on their first official date together, promising Betty Lou’s parents they’d be home by 11:00 PM. Shortly after that time, passing motorists saw the Rambler and its occupants parked at a lovers’ lane spot along Lake Herman Road in Benicia, California. Moments later, another driver noticed two seemingly lifeless bodies on the side of the road. Benicia police and others responded to the scene and discovered Betty Lou dead, with five bullet wounds in her back. David was found next to the Rambler with a bullet wound in his head, still breathing but near death. Bullet holes in the car’s roof and back window indicated that the killer may have fired warning shots to force the victims out of the vehicle. Shell casings recovered at the crime scene identified ammunition as Winchester Western Super X copper-coated. Ballistic evidence indicated that the killer used a .22-caliber, possibly a J. C. Higgins Model 80 semiautomatic pistol. Investigators believed the two teenagers were likely random targets killed by a stranger for unknown reasons.

Twenty-two-year-old Darlene Ferrin was a wife, mother and a popular waitress at a Vallejo restaurant. On the night of July 4, she picked up friend Michael Mageau and stopped her Corvair in the parking lot of Blue Rock Springs Park. Michael later told police that another vehicle pulled into the lot around midnight and then left only to return minutes later. The driver got out of the car, shined a bright light and fired into the Corvair with a 9mm handgun. Michael was shot in the jaw, shoulder and leg; Darlene was hit several times. At 12:40 PM, in a call later traced to a gas station pay phone, a man rang the Vallejo police department and claimed responsibility for the shooting as well as the murders on Lake Herman Road. According to the police dispatcher, the caller spoke in a low, monotonous voice, saying: “I want to report a murder. If you will go one mile east on Columbus Parkway, you will find kids in a brown car. They were shot with a 9-millimeter Luger. I also killed those kids last year. Goodbye.” Darlene died on arrival at the hospital, but Michael survived. Investigators were unable to identify any viable suspects.

1 – Letter to the Vallejo Times-Herald, postmarked July 31, 1969. The writer claimed responsibility for the two shootings and provided details about the victims, the weapons, the number of shots fired and the brand of ammunition.

2 – Letter to The San Francisco Chronicle, postmarked July 31, 1969. One of three virtually identical letters accompanied by one-third of a cipher. The writer demanded publication of the letters and ciphers by Friday, August 1st.

3 – Letter to The San Francisco Examiner, postmarked July 31, 1969. The writer threatened to kill again if newspapers did not publish the cipher, which included the words, “I like killing people because it’s so much fun.”

4 – Three-page letter received by the Examiner on August 4, 1969 Sent in response to police asking for information to prove the writer actually committed the murders, this was the first use of the name “the Zodiac.”

On a Saturday in late September, college students Bryan Hartnell and Cecelia Shepard were relaxing along the shore of Lake Berryessa, some 30 miles north of Napa, California. A man appeared holding a gun and wearing a hooded costume with a white crossed-circle stitched over the chest. Explaining that he had escaped from a prison and needed money and a car to escape to Mexico, the stranger bound their wrists with pre-cut lengths of plastic clothesline. Without warning, he plunged a large knife into Bryan’s back six times. He then stabbed Cecelia 10 times as she fought for her life. The man then walked to Bryan’s car, and used a pen to draw a crossed-circle on the door with the dates and locations of the previous attacks, the date “Sept 27 69,” the time “6:30,” and the notation, “by knife.” At 7:40 PM, a man called the Napa police department to report “a double murder.” The caller described Bryan’s car, directed police to the scene of the crime, and confessed, “I’m the one who did it.” Police traced the call to a pay phone at a car wash in Napa. Cecelia died two days later, but Bryan survived.

5 – Message written on the passenger door of victim Bryan Hartnell’s Volkswagen Karmann Ghia, which included the dates of the two shootings. Sherwood Morrill, the California Department of Justice documents examiner, concluded that the door message was written by the author of the “Zodiac” letters.

Paul Stine, a 28-year-old student and husband, worked as a cab driver in San Francisco. That night, Stine picked up a fare headed for a destination in the upscale Presidio Heights neighborhood. At the intersection of Washington and Cherry Streets, the passenger shot Stine in the head and removed a piece of the victim’s shirt. The man walked away just before the police arrived, but the police radio broadcast mistakenly described the suspect as a black man, and passing officers dismissed a white man resembling the correct description. Fingerprints found on the driver’s side of the cab may have belonged to the killer and a sketch was produced based on descriptions provided by witnesses. The case was considered a routine robbery until the office of The San Francisco Chronicle received an envelope with a letter from “The Zodiac” which began with the words, “I am the murderer of the taxi driver.” The envelope also contained a blood-stained piece of Paul Stine’s shirt. The Zodiac denied he left fingerprints and claimed the police sketch was inaccurate because he had worn a disguise.

6 – Letter to the Chronicle, postmarked October 13, 1969. The writer mocked police for failing to catch him and threatened to shoot children on a school bus. The envelope contained a piece of the blood-stained shirt belonging to victim Paul Stine.

7 – Envelope to the Chronicle, postmarked November 8, 1969, containing another piece of the cab driver’s shirt, a humorous greeting card and another cipher consisting of 340 symbols. The writer added, “Des July Aug Sept Oct = 7,” a possible reference to more unidentified victims.

8 – Seven-page letter to the Chronicle, postmarked November 9, 1969. The longest message from Zodiac claimed that police stopped him near a crime scene but let him go. Zodiac also included a bomb recipe and a diagram of the explosive.

9 – Letter addressed to famous attorney Melvin Belli, postmarked December 20, 1969. The writer feared he would kill again and asked Belli to intercede. The letter ended, “Please help me I can not remain in control for much longer.”

On a Sunday in late March, 22-year-old Kathleen Johns packed her infant daughter into a station wagon and left San Bernardino, California to visit her sick mother in Petaluma, in the northern part of the state. Kathleen was also seven months pregnant with the child of her long-time boyfriend. As she travelled on Highway 132 near Modesto, another vehicle pulled alongside the station wagon and the driver appeared to signal that Kathleen should pull over. On the side of the road, the driver explained that the back wheel of Kathleen’s station wagon was loose, but he promised to fix the problem. Instead, he loosened the lug nuts and the wheel fell off as Kathleen tried to drive away. The man then offered to drive Kathleen to a gas station, but she climbed into his car and discovered he appeared to have other plans. She claimed he also made veiled threats to harm her child. Eventually, Kathleen grabbed her daughter and jumped from the car. A passing driver took Kathleen to a nearby police station where she identified the stranger from a police sketch of the Zodiac. Months later, a Zodiac letter mentioned “a rather interesting ride” with a woman and her baby.

10 – Letter to the Chronicle, postmarked April 20, 1970. Included: a 13-symbol cipher and a diagram of a bomb designed to kill children on a school bus. The Zodiac denied responsibility for a recent police-station bombing that killed an officer.

11 – Greeting card to the Chronicle, postmarked April 28, 1970. Inside the card, the Zodiac demanded publication of his bomb threats and insisted that the people of the San Francisco Bay Area wear “Zodiac buttons” featuring his chosen symbol, the crossed-circle.

12 – Letter to the Chronicle, postmarked June 26, 1970, containing a map of the San Francisco Bay Area with a crossed-circle on the peak of Mt. Diablo and a code to locate the Zodiac’s bomb. The writer claimed he killed again.

13 – Letter to the Chronicle, postmarked July 24, 1970. The Zodiac complained that people weren’t wearing his crossed-circle “Zodiac buttons,” and he claimed that he was responsible for the failed abduction of pregnant mother Kathleen Johns on March 22, 1970.

14 – Five-page letter to the Chronicle, postmarked July 26, 1970. The Zodiac described torturing his victims and quoted from the Gilbert and Sullivan musical “The Mikado.” The letter also explained that the “Mt. Diablo code” concerned geometric angles known as “radians.”

A postcard attributed to the Zodiac featured an advertisement for a condominium project in Lake Tahoe, Nevada, with the phrases “pass Lake Tahoe areas” and “Sought Victim 12.” Some interpreted the cryptic message as a clue to the disappearance of 25-year-old Donna Lass. In May 1970, Donna worked in San Francisco at Letterman General Hospital, located on the Presidio military base near the area where the Zodiac killed a cabdriver. Donna moved northeast to South Lake Tahoe and found work as a nurse for the Sahara Hotel and Casino. On September 6, 1970, Donna vanished sometime after the last entry in her work logbook at 1:50 AM. Her car was later found abandoned near her apartment. According to some accounts, an unidentified man called Donna’s employer and her landlord, claiming she had to leave town due to a family emergency. Donna’s family told authorities there was no such emergency, and the man was never identified. Investigators suspected Donna had been abducted and killed, but her body was never found. Her disappearance remained a mystery and her name was added to long list of possible Zodiac victims.

15 – Suspected “Zodiac” postcard postmarked October 5, 1970, with a message constructed with text clipped from other sources. The words “The pace isn’t any slower! In fact it’s just one big” were clipped from the comic strip “Smidgens.”

16 – Halloween card sent to Chronicle reporter Paul Avery, postmarked October 27, 1970. The writer misspelled Avery’s name as “Averly,” and the number “4-teen” was interpreted as a possible reference to an unidentified 14th victim.

17 – Letter addressed to The Los Angeles Times, postmarked March 13, 1971. In it, Zodiac suggested he was responsible for the unsolved murder of Cheri Jo Bates near Riverside City College on October 30, 1966.

18 – Postcard to Chronicle reporter Paul Avery, postmarked March 22, 1971. The writer once again misspelled Avery’s name as “Averly.” The phrase, “Sought Victim 12,” was interpreted as a reference to the Donna Lass disappearance in Lake Tahoe, Nevada.

The search for new leads in the Zodiac case led investigators across the United States to Albany, New York. The office of the Albany Times Union newspaper received an envelope postmarked August 1, 1973, with a crossed-circle drawn in the corner instead of a return address. The letter read, “YOU ARE WRONG I’M NOT DEAD OR IN THE HOSPITAL I AM ALIVE AND WELL AND IM GOING TO START KILLING AGAIN Below is the NAME AND LOCATION OF MY NEXT VICTIM But you had Better hurry because I’m going to kill Her August 10th at 5:00 P.M. when the shift change. ALBANY is a nice town.” Below the message, the writer included three rows of symbols. According to an FBI report, bureau cryptanalysts deciphered the coded message to read, “[REDACTED] Albany Medical Center. This is only the beginning.” Investigators were unable to identify any murders that could explain the vague reference to a victim on August 10. Handwriting experts could not determine if the new letter was prepared by the writer of the Zodiac letters, “due to the lack of significant characteristics” in the Albany message, but this possibility could not be eliminated based on the limited analysis.

19 – Letter to the Chronicle, postmarked January 29, 1974. The writer alluded to a possible suicide in another quote from the Gilbert and Sullivan musical “The Mikado.” The notation “Me – 37, SFPD – 0” was interpreted as a “box score” indicating 37 victims.

20 – Postcard to the Chronicle, postmarked February 14, 1974. The writer referred to the SLA, or Symbionese Liberation Army, a group of militant urban guerrillas responsible for the abduction of newspaper heiress Patty Hearst. This message was signed, “a friend.”

21 – Card to the Chronicle, postmarked May 8, 1974. This message from “a citizen” complained about the “glorification of violence” in newspaper ads for the movie “The Badlands” about the killing spree by Richard Starkweather and his 14-year-old girlfriend.

22 – Letter to the Chronicle, postmarked July 8, 1974. The writer complained that Chronicle columnist “Count” Marco Spinelli suffered from a “serious psychological disorder” and should be sent “back in the hell-hole.” This letter was signed, “the Red Phantom.”