The detectives had intended to notify the rapper's family, but the report was released prematurely "due to an administrative error," the department said in a statement.
"Our detectives personally spoke with the Wallace family (Friday) night, and apologized for not notifying them prior to the release" said Capt. Billy Hayes, who heads LAPD's Robbery-Homicide Division, which is investigating the killing. "Obviously this has been a challenging case for us to solve. We hope that witnesses or other people with information will come forward and give us the clues we need to solve this case."
Los Angeles County's Chief Coroner Investigator Craig Harvey said a security hold placed on the report's release was lifted last week. The 23-page report revealed the rapper, whose real name was Christopher Wallace, was hit by four bullets after leaving a music industry event in March 1997, but one that hit his heart, left lung and colon caused his death.
The attorney for the rapper's family complained Friday that he was not given any notice that the report would be released and criticized police for not closing one of Los Angeles' highest-profile unsolved murders.
Both Los Angeles police and the FBI investigated Wallace's killing, which came just months after another rap superstar, Tupac Shakur, was gunned down in Las Vegas. The FBI looked into whether any Los Angeles police officers were involved in Wallace's shooting.
The deaths of Wallace and 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.
A 2011 book by former Los Angeles police detective Greg Kading claimed both murders had been solved, although no arrests have been made and federal prosecutors in 2005 declined to file charges after a lengthy, bi-coastal investigation. Wallace is from the New York City borough of Brooklyn.