On the eve of what would have been Tupac Shakur's 40th birthday, an imprisoned man has admitted to shooting the late rapper/actor during a robbery at Manhattan's Quad Studios in November 1994. What's even more startling is that the alleged triggerman, Dexter Isaac, is claiming in a letter that was obtained by AllHipHop.com that 'Pac's former associate, Jimmy "Henchman" Rosemond, paid him $2,500 to do the deed.

While this may be a revelation to some, 'Pac's former protégé and Outlawz member E.D.I. Mean told MTV News that he was well aware.

"It's not news for us, because this is information that we been had and that been knew about. And we always knew that it'll come out one day, because what's done in the dark always comes to light," he said before pointing to Shakur's music as proof. "I just feel like it's verification for what 'Pac said, because a lot of people felt when 'Pac was saying what he was saying on Makaveli that he was out of line for saying that."

The specific lyric E.D. is referencing is from "Against All Odds," a fiery track that appeared on Tupac's The Don Killuminati: The 7 Day Theory album (commonly referred to as the Makaveli album). On the song, the now-deceased MC implies that Henchman set him up in 1994 as he raps: "And did I mention promise to pay back Jimmy Henchman in due time/ I know you bitch n---as is listenin', the world is mine/ Set me up, wet me up, n---as stuck me up/ Heard the guns bust, but you tricks never shut me up."

Ultimately, E.D.I. Mean believes that Isaac's confession will eventually help the authorities solve the 1996 murder of Shakur as well as the 1997 shooting death of the Notorious B.I.G. — two crimes that many feel are related. "This will go on for a little bit longer, and I really feel like it's a domino effect," he said. "This will really lead up to their actual murderers. Both Big and 'Pac and everybody can move on, and this will be like some closure for not only the families, but the whole hip-hop community, because it's been an open wound since 1996 and 1997."

In a 2008 interview with MTV News, Rosemond denied any involvement in the 1994 shooting and dismissed the song as a shock tactic that rappers often use. "Absolutely never [had I] even know about it, never heard about it — before, afterward — had nothing to do with it," Rosemond added about the ambush. "Nobody that I know [was] associated with [the attack], and this is why I have confidently, in the last 14 years, told people that they can dig up whatever they want to dig up. And I've been very firm in what I've said to people: that I've had nothing to do with it."

Isaac, who is currently serving life in prison for murder, robbery, fraud and witness-intimidation charges, tells a different story. "I want to apologize to his family [Tupac Shakur] and for the mistake I did for that sucker [Jimmy Henchman]," Isaac told AllHipHop.com from prison. "I am trying to clean it up to give [Tupac's and Biggie's] mothers some closure."

Rosemond himself is facing legal trouble. On May 17, news broke that federal authorities issued an arrest warrant for Henchman in connection with a drug case. Henchman, who runs Czar Entertainment, a company that manages the career of the Game and other rap artists, fired back in a letter, lashing out at the "slanderous media" coverage he has received about the case. He also went on to call out Isaac's credibility. "If the government is relying on informants like Winston 'Winnie' Harris, a convicted drug dealer and Jamaican deportee, who came to me and motioned via hand signal that he was forced to wear a wire and begged me to skip town, or Dexter Isaac, who is serving life in prison plus 30 years, then I'm sure I will not be offered a fair trial."

Take a look back at what Tupac told MTV News about the idea of being a "role model," and celebrate his birthday on the Rapfix blog.

Check back with MTV News for updates as this story develops.