A detective who investigated the murder of Biggie Smalls and concluded the rapper was killed by police officers working with Suge Knight has suddenly died.

Retired LAPD detective Russell Poole collapsed on Wednesday while meeting with detectives about a cold case, reports the Los Angeles Times.

It is thought he had a heart attack.

Poole worked for about a year on the case and eventually advanced the theory that three police officers were responsible for the murder along with Biggie's arch enemy, the CEO of Death Row Records, Marion 'Suge' Knight.

'You got to think to yourself, 'Who could do this and get away with it?' Cops,'' he reportedly said in the 2002 Nick Broomfield documentary Biggie & Tupac.

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Russell Poole, the former LAPD detective best known for his involvement in rapper Biggie Small's murder case, died suddenly Wednesday from a possible heart attack. Poole appeared in 'Biggie & Tupac' a documentary about the murders

Notorious B.I.G., also known as Biggie Smalls, was killed at 24 but his murder has never been solved - Russell Poole was lead detective on the case

Notorious B.I.G, 24, who had catapulted to fame with his album Ready To Die, and who was involved in a notorious 'East Coast-West Coast' dispute with various hip hop figures, was sitting in Los Angeles traffic after an awards party when he was shot by someone in another vehicle.

Also in Biggie's car were members of the Junior M.A.F.I.A. hip hop group. In a nearby car was Bad Boy Records CEO Sean 'Puff Daddy' Combs.

Smalls was hit five times and was killed.

One of the officers who Poole accused of being involved in the killing is David Anthony Mack, who would later serve 14 years in prison for robbing a bank.

Mack reportedly worked as Knight's bodyguard and grew up in the same neighborhood. He has always denied being involved in the murder. A civil case was brought against the LAPD by Smalls' estate in 2007 but the suit ended up being dropped.

Notorious B.I.G. and Sean 'Puffy Daddy' Combs at the The 11th Annual Soul Train Music Awards - Biggie would be killed later that night

Detective Poole (above) advanced the theory that Smalls was killed by three corrupt LAPD officers who were working with Suge Knight - but his theory was shot down by the LAPD

Poole claimed that LAPD officer David Mack (pictured) had links to the murder of Smalls - Mack was never charged but served 14 years in prison for a bank robbery

Poole suggested that Mack and Knight conspired to kill Smalls as retaliation for the murder of rapper Tupac Shakur, which had happened six months previously. Shakur was on Knight's record label, which was seen as a rival to Combs' record label, which Smalls was on.

Knight was never implicated in Smalls' murder but spent nine years in prison on a probation violation. He was released in 2001 but arrested again in 2015 on suspicion of murder charges.

When Poole presented his findings to the then-chief of the LAPD, Bernard C. Parks, he was reportedly ordered to stop the investigation. As a result, he resigned in 1999.

He filed a lawsuit against the LAPD for violating his First Amendment rights for not allowing him to go public with his information. His suit was dismissed, according to the New York Times.

He eventually opened his own detective agency.

Poole was also the main subject of the book. 'LAbyrinth: A Detective Investigates the Murders of Tupac Shakur and Notorious B.I.G., the Implication of Death Row Records' Suge Knight, and the Origins of the Los Angeles Police Scandal.'

Russell had a long and illustrious career that also included shining a spotlight on the late-90s Rampart Scandal, which uncovered widespread police misconduct throughout the LAPD's Community Resource Against Street Hoodlums (CRASH) unit.

He also revealed that many cops were working security for Death Row records, including David Mack, according to Vice.com.

Rapper Tupac Shakur (left) and Suge Knight (right) were supposedly in a beef with Smalls and Sean Combs - theories abounded that Shakur's and Smalls' murders were linked to the bad blood between them

Happier times: Rappers Notorious B.I.G., (left) Tupac Shakur (center) and Redman (right) pose for a 'bad boy' backstage at Tupac's show at the Palladium on July 23, 1993

Poole (above) had also advanced the theory that Shakur's murder was a conspiracy involving Knight's then-wife and the head of security for Death Row Records - neither were ever implicated

Biggie Smalls (left) was supposedly enemies with Suge Knight (right) who ended up going to prison for nine years on unrelated charges - he is currently charged with suspicion of murder in another case and remains in jail on $10million bond

In an interview with Vice in June, Poole theorized that Shakur's murder was orchestrated by Suge Knight's then-wife, Sharitha Knight, and Reggie Wright Jr., head of Death Row Security.

Knight was in the car along with Shakur the night he was killed, and was also shot, but survived.

'Suge wasn't divorced yet and if he died in that hit, she'd get most of everything,' Poole speculated. 'So she went to Wright Jr., who was in charge of Death Row and ran it while Suge was in prison.'

Neither Sharitha Knight nor Reggie Wright have ever been implicated in Shakur's murder.