A startling "confession letter" is said to be the final key in solving the 1996 murder of Tupac Shakur.

US documentary maker and author RJ Bond claims a document names his killers, and clears rap mogul Suge Knight of any involvement in the September 13 drive-by shooting, the Daily Mail reports.

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• Suge Knight claims his ex-wife and former Death Row Records security chief killed Tupac

It also is said to point a finger at two separate rappers (who are unnamed) and Death Row Records security chief Reggie Wright Jnr, who is said to have ordered the drive-by shooting.

The letter, obtained by The Sun, was allegedly written by one of the gunmen who opened fire on Tupac's car that night in Las Vegas.

Someone called "Danny" is said to have handed the letter to a TV journalist. The letter, which is unverified, says Danny was "told to take night out," referring to Death Row Records boss Suge Knight, who many believe were behind Tupac's death.

Knight was with Tupac in the Cadillac the night he was shot.

Tupac's last public photograph was taken as he was riding in the car with Death Row Records co-founder Suge on September 7, 1996, in Las Vegas.

The pair had just left a Mike Tyson fight held at the MGM Grand, when the 25-year-old rapper was shot as he stood up through the sunroof to talk to a group of women while the car was stopped at a traffic light.

Shakur was hit four times - twice in the chest, once in the arm, and once in the leg. He eventually died six days later on September 13.

There was a major problem with demo stealing. Two songs that Tupac came out with were written by XXXX XXXXX. XXXX XXXXX was an up and coming rap singer. He gave four demos to Tupac to look over because he met Tupac at the Bonaventure hotel (Los Angeles). Tupac promised that he would look over the demos. XXXX XXXXX never heard from Tupac and three months later, after Tupac received the demos the song Brenda's Got a Baby was released. Brenda's Got a Baby was written by XXXX XXXXX. XXXX XXXXX let that slide, but he continued to go to different recording studios. Finally in '94, XXXX XXXX started making money. And he was sponsored mostly by [Suge Knight].What [Knight] did not know was that XXXX XXXX found out that he was being sold to XXXXX. There was a meeting in Reno. And XXXX XXXX and Tupac had a dispute about songs that were taken. XXXX XXXX was beaten down by Tupac soldiers. As days went by there were meetings with [gangs;] ICG, Gear Gang, Ghost Town, Front Street, 52 hoovers and South Park. A bounty was put on Tupac and Knight. Mr. [Wright] Jr. gave info where Tupac was going to be. There were six different barricades that no matter what would have happened no one would have made it out. I was the shooter that was told to take Knight out. XXXX XXXXX was the one that took Tupac out. As for gun that was used, [it] will be dropped off at the security booth at Fox 11. Please do not have stop or talk to one of dropping off the gun.

The letter, written in chilling detail, details the assassination, and says that "no one would have made it out," going on about the background of a stolen rap song, a gang beating and the revenge murder.

It seems to point a finger at Death Row Records security chief Reggie Wright Jnr, and another up-and-coming rapper who cannot be named for legal reasons.

The letter says that Wright told the shooters where Tupac would be on the night of his assassination, and that the rapper opened fire.

Bond says: "The story behind the confession letter is very simple. It was given to a Fox reporter who was very keen on the story.

"A big TV interview was set up by he was a no show and the letter was then given to Russel Poole (a former LAPD cop) and was put in a file and not looked at for a long time. When I saw it, the name of Reginald Wright Jrn just leaps out of the page. It reads he gave Tupac's location. My jaw just hit the floor when I read that".

Bond is currently working on this third documentary covering the murder mystery.

He told the Sun: "This letter is a bit like the Rosetta Stone - it makes a lot of other things make sense.

"This new documentary is important for all those involved in the killings, but in particular the victims and witnesses like Yafue Fula, the Outlawz rapper who was shot after the Tupac killing.

"The night of the Tupac shooting he was nearest to the Cadillac and gave a statement to Las Vegas cops of the driver of the shooters' car. When we saw a picture of Danny he matched the description of the driver. I mean, what are the chances".

Wright Jrn has long denied ties to Tupac's death, and in 2015 responded to claims by pointing out that people that have linked him to Tupac's murder have died in the past decade.

Those people include Tupac's ex-bodyguards Michael Moore and Frank Alexander.