Rapper Keefe D - whose real name is Duane Keith Davis - has spoken about being a witness to the murder, 22 years after the drive-by shooting in Las Vegas.
Davis describes Tupac as standing up through the roof of the BMW when he was shot
He died from his injuries six days later.
Davis, who has been diagnosed with cancer, has chosen to speak now due to his illness granting him immunity from prosecution.
In a documentary, Davis describes how he was a front seat passenger in the white Cadillac from which the fatal shots were fired.
Davis says the car was driven by Terrence "T-Brown" Brown, while DeAndre "Dre" Smith and Davis's nephew Orlando "Baby Lane" Anderson were in the back seat.
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All the men were part of the Southside Crips gang and Brown, Smith and Anderson have since died.
Davis says they had been looking for Tupac - who he alleges had beaten up one of their fellow gang members - at the 662 club, owned by Death Row Records boss Marion "Suge" Knight, who was known to be with Tupac that evening.
However, he says after leaving the club without finding Tupac, they saw him in a BMW standing up "like a celebrity in a parade" through the open top of the car.
He goes on: "If he wouldn't even been out the window, we would have never seen him."
When directly asked who fired the shot, Davis answers with a smile: "Going to keep it for the code of the streets. It just came from the back seat, bro".
For Madonna, being "with a black man wouldn't jeopardise" her career, the letter says, but things were different for the rapper.
However, in a previous recorded police interview Davis identifies his nephew Anderson as the gunman, saying he "leaned over" and fired from the right-hand side of the car.
Anderson - who died aged 24 in an unrelated gang shooting in 1998 - had previously denied the claim.
Kyle Long, the executive producer of the documentary, has criticised the LAPD for taking no action, despite Davis confessing to be an accessory to murder.
Previously, links have been made between Tupac's shooting and that of fellow rapper The Notorious B.I.G. - also known as Biggie Smalls - in March of the following year.
There have been no prosecutions for either killing.