The autopsy said so. He was not asphyxiated. He had a heart attack.
The autopsy also said it was murder.
No, it didn't. It said it was "homicide", which is NOT the same thing. They're used interchangeably by people with sloppy English skills, but they actually have two separate definitions, which may or may not coincide. This is why we also have the term "justifiable homicide" in the law, for killings in self-defense.
In legal terminology, "homicide" is a death that involves another person, as in it wasn't natural causes, disease, or suicide. "Murder" denotes specifically
illegal killing of one person by another person.