For 51 years, one of the Zodiac Killer’s puzzling codes he sent in letters to newspapers in the late 1960s and early 1970s has confounded the cryptography community, law enforcement and curious citizens.

But the Bay Area killer’s 340-character cipher mailed to the San Francisco Chronicle has been cracked by an international team of code-breakers. The breakthrough, first reported by the Chronicle, was verified by the FBI.

“I felt vindicated,” said American code-breaker David Oranchak, who told The Washington Post that he first saw the cipher 14 years ago and thought he could decipher it quickly.

Along with Australian mathematician Sam Blake and Belgian programmer Jarl Van Eycke, the trio figures the grid of 63 unique, mysterious symbols, written by the killer and mailed to the Chronicle with a victim’s bloodstained shirt, roughly translates to:

I HOPE YOU ARE HAVING LOTS OF FUN IN TRYING TO CATCH ME
THAT WASNT ME ON THE TV SHOW
WHICH BRINGS UP A POINT ABOUT ME
I AM NOT AFRAID OF THE GAS CHAMBER
BECAUSE IT WILL SEND ME TO PARADICE ALL THE SOONER
BECAUSE I NOW HAVE ENOUGH SLAVES TO WORK FOR ME
WHERE EVERYONE ELSE HAS NOTHING WHEN THEY REACH PARADICE
SO THEY ARE AFRAID OF DEATH
I AM NOT AFRAID BECAUSE I KNOW THAT MY NEW LIFE IS
LIFE WILL BE AN EASY ONE IN PARADICE DEATH

The code does not uncover the long-sought identity for the man behind a string of murders in Northern California at that time.

Sent in 1969 after a schoolteacher and his wife cracked the Zodiac Killer’s first cipher, the 340-character cipher was more complex and remained unsolved, even by a supercomputer designed to think like the killer. Experts believed it was a transposition cipher but were mystified by the arrangement of strange markings.

The trio of amateur sleuths have worked on the puzzle for a year using Van Eycke’s code-breaking computer program and more than 650,000 variations written by Blake. The shocking discovery came Dec. 3, Oranchak said in a YouTube video published Friday.

Oranchak was feeding the variations into the program when he noticed one solution had phrases like “hope you are” and “trying to catch me” in the gibberish.

Oranchak changed the code-breaking program’s settings to recall those phrases and solve the rest, which gave him a clearer line of text. When he saw “that wasn’t me on the TV,” Oranchak said he jumped from his chair.

Two weeks before the letter was sent, someone claiming to be the Zodiac Killer called a morning TV news show hosted by Jim Dunbar, saying, “I don’t want to go to the gas chamber.”

By Saturday, the team had solved it and sent its answer to the FBI, which is still investigating the case.

“The FBI is aware that a cipher attributed to the Zodiac Killer was recently solved by private citizens,” spokeswoman Cameron Rogers Polan said in a statement. “The Zodiac Killer case remains an ongoing investigation for the FBI San Francisco division and our local law enforcement partners.”

Oranchak said all of this resulted from a hobby.

“So to actually come upon the answer, and feel like it’s right based on our knowledge of cryptography and then submit it to the FBI and have them verify it, it was a very good feeling.”

Read more: