One of the Zodiac Killer’s most elaborate cryptograms has finally been solved 51 years after it was sent to The San Francisco Chronicle. The mysterious serial killer, who has never been caught, is believed to be responsible for at least five murders in the Bay Area in the late 1960s. He gained his pseudonym from creepy letters he sent to local newspapers, often including cryptograms.

The so-called 340 Cipher baffled observers for years but was finally solved by an international code breaking team from the U.S., Australia and Belgium, the Chronicle reports. It reads: “I hope you are having lots of fun in trying to catch me. ... I am not afraid of the gas chamber because it will send me to paradise all the sooner because I now have enough slaves to work for me.” Unfortunately, it doesn’t offer any obvious clues about the killer’s identity but the FBI said it was aware of the breakthrough and its investigations were ongoing. One other cryptogram from the Zodiac Killer said, “I like killing because it is so much fun.”