A team of volunteer codebreakers has cracked a mysterious cipher sent more than 50 years ago to a newspaper by the San Francisco serial killer who called himself the Zodiac, the FBI said on Friday.

The Zodiac Killer — who was never caught — shot or stabbed seven people in the San Francisco Bay Area over the course of about year in 1968 and 1969, killing all but two of them. During his murderous spree, he sent a series of terrifying letters to the San Francisco Chronicle newspaper.

Some of the notes were in code, including a particularly complex missive with 340 characters that became known as the 340 cipher.

“I hope you are having lots of fun trying to catch me,” said the cipher, cracked last week by codebreakers David Oranchak, Sam Blake and Jarl Van Eycke, according to a video posted on YouTube by Oranchak. “I am not afraid of the gas chamber because it will send me to paradice (sic) all the sooner because I now have enough slaves to work for me.”

Like the murders themselves, solving the Zodiac ciphers has become an international fixation for true-crime followers.

Oranchak, whom the San Francisco Chronicle identified as a 46-year-old Web designer who lives in Virginia, said in the video he had hoped the cipher would yield information about the killer’s identity. “The message doesn’t really say a whole lot,” he said.“It’s more of the same attention-seeking junk from Zodiac.”

The San Francisco office of the FBI on Friday confirmed that the group had cracked the coded message, and said the investigation into the half-century-old case was ongoing.

“The FBI is aware that a cipher attributed to the Zodiac Killer was recently solved by private citizens,” the FBI said.

The case has inspired numerous books and movies, including 1971’s Dirty Harry starring Clint Eastwood and 2007’s Zodiac with Robert Downey Jr.