A coded message sent by the infamous Zodiac Killer more than half a century ago has been cracked, the FBI has announced.

The Zodiac Killer, who was never identified, shot or stabbed seven people in the San Francisco Bay Area between 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 letters sent were written in standard English, others were written in code. One particularly complex missive containing 340 characters, received in November 1969 and which became known as the 340 cipher, had never been cracked.

But now, a video posted to YouTube appears to have solved the mystery.

“I hope you are having lots of fun trying to catch me,” said the cipher, cracked last week by amateur code-breakers David Oranchak, Sam Blake and Jarl Van Eycke. 

“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.”

The misspelling of the word “paradise” throughout the piece helped the decoders and the FBI identify that the letters were indeed sent by the Zodiac Killer, as this error also featured in the other letters.  

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

Mr Oranchak, 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 in a statement posted on Twitter.  

“The Zodiac Killer terrorised multiple communities across Northern California, and even though decades have gone by, we continue to seek justice for the victims of these brutal crimes.”

No one was ever charged in the Zodiac case, and theories abound as to the killer’s real identity. The case has inspired numerous books and movies, including 1971’s Dirty Harry starring Clint Eastwood and 2007’s Zodiac with Robert Downey Jr.