The stuff we know. I wouldn’t doubt if they took a blood sample. Heart attacks leave behind chemical traces in the bloodstream, very easy to detect (actually sometimes the ONLY detectable thing, my uncle was in the hospital for 2 weeks having silent heart attacks the whole way, he had some symptoms to start but they went away shortly after he got to the hospital, doctor wouldn’t release him until the blood work came back clean). There are ways short of an autopsy to detect many forms of death, these are the things they generally use to decide whether or not to do an autopsy. People need to stop seeing boogiemen behind every corner, fat old people die, it happens.
Justice Scalia’s family said no to an autopsy.
Hey - the bodies of Supreme Court Justices are found everyday, no biggie. No need to inspect the body, just phone it in.