A medical examiner's office on Monday ruled that the death of George Floyd, the black man whose killing in Minneapolis police custody last week triggered nationwide protests, was a homicide and that he died from asphyxiation.

The medical examiner’s finding that the death was a homicide confirms the same conclusion of the independent autopsy that was also released on Monday, but there are key differences over the cause.

A press release from the Hennepin County Medical Examiner said that Floyd, who struggled to breathe as an officer pinned him down by kneeling on his neck, had “recent methamphetamine use” and “fentanyl intoxication” — along with hypertension and coronary artery disease — all of which were possible contributing factors to his death.

But two doctors who carried out that independent autopsy of Floyd, 46, and two attorneys for the family said that he had no underlying health conditions that may have contributed to his death.

They argued that not only the officer who was kneeing Floyd’s neck killed him, but also two officers who were pressing their weight onto Floyd’s back while he was on the ground.

They added that they did not have information on toxicology and any drug or alcohol use by Floyd.

Dr Allecia Wilson of the University of Michigan, one of the two forensic doctors who performed the independent autopsy, said the evidence pointed to homicide by “mechanical asphyxia” meaning from some physical force that interfered with oxygen supply.

While the county’s full autopsy report has not yet been released — Monday’s press release appeared to show authorities walked back their conclusions on what killed Floyd.

The original criminal complaint against the police officer who pinned Floyd with his knee cited the medical examiner’s office when it said it found no findings of strangulation.

Carolyn Marinan, a spokeswoman for Hennepin County, did not confirm any reversal, saying only that Monday’s press release were the “final findings.”

Baden has worked on several high-profile cases, including the 2014 death of Eric Garner.