An independent report into the police shooting of an unarmed black teenager in California is finally to be published after a three-year battle.

Kendrec McDade, 19, was shot dead on the street in Pasadena in 2012 by two police officers. The officers believed McDade had been involved in the theft of a laptop at gunpoint, although no weapon was ever found and the victim of the robbery later admitted he had lied to police about the gun in order to get them to respond faster.

A report into the police officers’ actions conducted by the Office of Independent Review (OIR), a civilian oversight group, has never been made public despite a lengthy battle by McDade’s mother, Anya Slaughter, and civil rights organisations.

In an exclusive interview with the Observer last week, Ms Slaughter accused the police of a cover-up and said they had “assassinated my son”.

The administration promised full transparency. Instead, when the report was belatedly delivered in August 2014, it was announced that only its recommendations would be made public.

But a California appeals court ruled last month that 80% of the report should be made public. The Pasadena Police Officers’ Association (PPOA) had until last Tuesday to file a petition for review to appeal but did not do so. The OIR report will now be published in about four to eight weeks.

Dale Gronemeier, a civil rights lawyer acting for McDade’s mother, said: “The PPOA’s throwing in the towel on this case is a wise decision … Moreover, the odds would have been very long ones for the PPOA to get anywhere with a petition for review; the supreme court has strict standards for what cases it takes.”

Gronemeier added that the Observer’s piece last week was: “the best article that has ever been written about Kendrec’s shooting … It is a tribute to the Observer’s journalistic standards that an English reporter could drill down and write the compelling account that the Observer published.”