Dunno. I'm just puzzled. It's a "homicide" investigation.
"Negligent homicide" is the killing of another person through gross negligence or without malice. Could be that. "Friendly fire" for those enduring it is regarded by them as pretty goddamned gross negligence which doesn't get much grosser.
Homicide is the intentional killing of another person. The report I read said "homicide", and could, I'm sure, include both forms.
Anything else would be on the order of, in civilian terms, manslaughter.
Arf