A post-mortem examination of the helicopter crash that killed basketball star Kobe Bryant has ruled blunt force trauma as the cause of death for all nine victims.

The 180-page report also found that the pilot, 50-year-old Ara Zobayan, tested negative for drugs and alcohol.

The cause of the 26 January crash, which occurred in California amid heavy fog, is still being investigated.

Bryant's 13-year-old daughter, Gianna, was with him on board the helicopter.

The passengers - which included two of Gianna's basketball teammates, their relatives and a coach - were on their way to a tournament in Thousand Oaks where Bryant had been set to coach.

Alyssa Altobelli, John Altobelli, Keri Altobelli, Sarah Chester, Payton Chester, Christina Mauser all died alongside the Bryants, and pilot Ara Zobayan when the helicopter crashed into a hill just north of Los Angeles.

"On Jan. 28, the cause of death for all nine victims was ruled as blunt trauma," the examination said. "The manner of death was certified as an accident".

The results of the post-mortem examination were posted on the website of the Los Angeles County Medical Examiner-Coroner office on Friday.

Bryant, a five-time NBA champion, played for the LA Lakers throughout his career and is considered one of the greatest players in the game's history.

He retired in April 2016 after a 20-year career with the team.

Lawyers for his widow, Vanessa Bryant, have filed a lawsuit against the company that operated the helicopter.

It alleges that Zobayan - who died in the crash - did not assess weather data before taking off.

Separately, earlier this year, the sheriff of Los Angeles County said eight deputies had admitted possessing graphic photos of the crash site.

Alex Villanueva said he was "devastated and heartbroken" by their conduct. He said he had instructed the deputies to delete the images.