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Fayçal Ziraoui claims that he managed to solve a mystery in just 14 days that has plagued experts for more than 50 years.
He started his short quest when he spotted an article in a French magazine talking about how no-one had managed to solve the cipher left by the killer as he wrought a path of terror through the San Francisco Bay Area back in the 1960s and 1970s.
So, he thought 'why not me?' and gave it a go, despite the fact that most people in the know believe no-one would ever be able to figure it out.
The 38-year-old claims that he used the encryption key which only became available in December, and a number of code-breaking skills, including a program of his own devising, to break the cipher in two weeks.
He then went to reveal his findings to the online community, but was met with anger, abuse, and disbelief.
Code-breaking boffins rejected his hypothesis, and one of his posts was even deleted by a community moderator.
One said: "I don't believe it for a second."
Another wrote: "When he says that it took two weeks to crack the Z32 and an hour for the Z13, I think that sums it up pretty well."
His brother, Youssef, who works as a journalist, told the New York Times: "He came in and told them 'end of the game'. But these people don't want the game to end."
The FBI haven't commented on the findings that Ziraoui sent to them, either.
The two pieces of code he says he deciphered are known as Z32 and Z13.
They were left behind by whoever the killer was. He - or she - killed at least five people back in the day, but boasted of having killed 37 people.
According to Ziraoui, Z32 gives the co-ordinates for a school that the killer put a bomb in, and Z13 reveals the killer's name.
He said: "I was obsessed with it, 24 hours a day, that's all I could think about."
After two weeks, he managed to get the message: "LABOR DAY FIND 45.069 NORT 58.719 WEST."
That's a school near South Lake Tahoe in California that the killer had referred to in the past.
After an hour with Z13, he came up with 'KAYR' which he believes to be a reference to Lawrence Kaye, a man who was suspected of the murders, but nothing was ever proven.
Ziraoui believes it's simply too coincidental not to be true.
Mr Kaye, who also adopted the pseudonym Kane, was the subject of a report by Detective Harvey Hines, but he couldn't convince superiors to take it further.
Despite Ziraoui's best efforts, the mystery may continue forever.