Fall 2015 will mark 19 years since Tupac was murdered on the Las Vegas strip.

Theories have surfaced for years as to what happened on the night of Sept. 7, 1996, when he was killed. The "California Love" rapper's murder remains unsolved.

Now, a former Los Angeles Police Department detective, Russell Poole, says that he knows who was behind 2Pac's murder, reports XXL magazine.

XXL and Vice contributor Jeff Weiss reports that in 1998, Poole received a tip from a local crime reporter about a man named Malcolm Patton who supposedly confessed to carrying out a hit on the "All Eyez on Me" rapper. The tip was communicated by one of the writer's jail informants. According to the informant, Patton said that he, his brother and a Long Beach Crip named Donald Smith planned the hit with help from Reggie Wright, Jr., the head of Death Row security, and Suge Knight's then-wife.

Poole served as the main source in Randall Sullivan's investigative book "LAbyrinth," which follows the detective as he investigated the murders of Tupac and Notorious B.I.G. The book also explores the implication of Death Row Records' Suge Knight, and the origins of the LAPD scandal.

Smith, who is also known as the rapper Lil 1/2 Dead, is a Death Row affiliate and Snoop Dogg's cousin. He allegedly had a personal motive for killing the "Hit Em Up" rapper: Poole claims that in 1991, during the recording of "2Pacalypse Now," Smith was an aspiring rapper who gave 2Pac his demo tape. Smith never heard from 2Pac regarding the demo, but he did hear his lyrics on the radio in the Tupac's breakthrough hit "Brenda's Got a Baby." Lil 1/2 Dead allegedly wrote the lyrics, and was furious.

Poole, a revered detective, has expressed both anger and disappointment that law enforcement mishandled the investigation. "If this was Elvis Presley and Frank Sinatra who got murdered, there would've been arrests a long time ago," he told Weiss. "This case can be solved, but needs police follow-up. There are clues sitting right in front of the police. It's a travesty of justice."

Despite Poole's information, Sullivan believes someone else shot Tupac. "I still think the shooter was who everyone thinks it was: Orlando Anderson," he told Weiss.