Notorious B.I.G. was killed by a single bullet that pierced several vital organs in a 1997 drive-by shooting, a long-sealed autopsy report released Friday shows.

The rapper was hit four times in the shooting, which 15 years later remains one of Los Angeles' highest-profile unsolved murders.

The report had been sealed at the request of detectives until last week, Chief Coroner Investigator Craig Harvey said. The 23-page report details the trajectory of each shot that hit the rapper, whose name was Christopher Wallace. Investigators determined that a single shot that hit his left lung, heart and colon led to the 24-year-old's death. No drugs or alcohol were found in his system, the report states.

The rapper from Brooklyn, N.Y., had just left a music industry event when he was shot. Los Angeles police and the FBI have investigated the killing, but no arrests have ever been made.

A lawyer for Wallace's family and widow Faith Evans did not immediately return a message seeking comment.

Federal agents conducted a bi-coastal search for Wallace's killer, but federal prosecutors determined in 2005 that there wasn't enough evidence to pursue a case. Agents also looked into whether any Los Angeles police officers had been involved in the shooting.

In March 2011, the FBI electronically released files on its investigation, which were heavily redacted but shed new light on the efforts that investigators took to try to find those responsible for the rapper's death. Agents conducted surveillance and interviews in Los Angeles, San Diego and New York, the files showed.

The deaths of Wallace and Tupac Shakur have been the subject of rampant speculation about the motives. The one-time friends became rivals and instigators in an East Coast-West Coast rap rivalry during the mid-1990s.

Wallace's family filed a federal lawsuit against Los Angeles, and a 2005 trial ended with a mistrial after attorneys for Wallace's family discovered the city had withheld a trove of LAPD documents.

The family dismissed the lawsuit in 2010. Their attorney said that was done in order for the FBI and other agencies to pursue new leads in the case.

The civil case could be refiled, although that has not yet occurred.