I'm having trouble wrapping my head around any kind of "murder". The best I can fathom is a low level manslaughter charge, and involuntary or reckless at that. Frankly, I think the whole case stinks.
I’ve never heard of third degree murder. Murder, at common law, is the unlawful killing of a human being with malice aforethought. In most US jurisdiction, it is “first degree” if it is also premeditated — but “premeditation” doesn’t mean it was planned for a long time; it can be a mere moment’s malicious planning. So even lawyers often have difficulty deciding whether a murder is 1st or 2d degree.
Manslaughter — perhaps that is what was meant by M3? — also comes in two flavors. Voluntary manslaughter typically is “what would otherwise be a murder,” but committed in a heat of passion caused by a provocation that would cause a reasonable person (and DID cause the defendant) to lose control. Involuntary is — again, speaking off the cuff here — when your incredibly stupid, reckless conduct accidentally kills someone.