A programmer from Belgium, a mathematician from Australia, and a cryptologist from the United States cracked the code just last weekend.
ABC7 I-Team reporter Dan Noyes spoke with members of that international team.
From his home in Virginia, David Oranchak, told the I-Team, "By Saturday morning, we had a pretty good idea what the full message was, and then I contacted the FBI and within minutes, they confirmed the solution to me."
According to Oranchak, the cipher attributed to the killer says, "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."
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One of the lines that first appeared from the cipher was a major clue: "That wasn't me on the tv show."
Someone claiming to be the Zodiac had called into the KGO morning show in 1969, telling host Jim Dunbar and attorney Melvin Belli, "I want to kill those kids."
Oranchak explained, "So that's what really stood out. And that's when I knew, okay, this has got to be something real. And that's when my heart rate just really shot up."
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In a statement to ABC7 News on Friday, the FBI confirmed they were aware the cipher had been solved by "private citizens."
The agency said the case remains an "ongoing investigation."
"The Zodiac Killer terrorized multiple communities across Northern California and even though decades have gone by, we continue to seek justice for the victims of these brutal crimes. Due to the ongoing nature of the investigation, and out of respect for the victims and their families, we will not be providing further comment at this time," the FBI said.
In December 1968, the Zodiac Killer killed two teenagers on Lake Herman Road in Benicia. A couple was later shot in July 1969 while parked at Blue Rock Springs Park in Vallejo. One of the victims died.
In September of that same year, a masked suspect stabbed two people at Lake Berryessa, killing one of them.
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In October 1969, a San Francisco cab driver was shot and killed.
The Zodiac Killer's identity has remained a mystery for decades. Investigators had hoped a cipher would reveal the killer's name, but that is not the case in the 340.
You can watch a video in which Oranchak explains how they cracked the cipher here.
Take a look at for a look at more stories by Dan Noyes and the ABC7 News I-Team.