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.

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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".