A police officer who was working on the Tupac Shakur murder case has revealed in a new documentary that the gun used to kill Tupac was found but then went missing.

Deputy T Brennan has told 'Who Killed Tupac?' documentary makers that the gun was reported to the Compton Police Departement but the LA County Sheriff's Department took over jurisdiction and confiscated 3,800 firearms, which included that gun.

The .40 caliber Glock gun was in the home of a girlfriend of a Crip gangmember who had fallen out with Tupac.

'Who Killed Tupac?' is a six-hour series, focusing on the investigation, twenty years after the death of the prolific and influential rapper and actor, Tupac Shakur.

Each installment of the investigative series includes aspects from the legendary artist’s life, and follows the civil rights attorney Benjamin Crump as he conducts a full-scale intensive investigation into key theories behind his murder.

The final episode airs on December 19, and can be streamed live on A&E online. 

Tupac was shot four times in Las Vegas in September 1996. He was only 25 years old at the time. Shakur sold over 75 million records worldwide.