The Gov. must prove Intent. Tough to prove what was in someone's mind.
Example. Murder trial:
Bill admits he shot John.
Bill says it was an accident, and didn't know weapon was loaded.
Plausible defense...BUT
Witness saw Bill chamber a live round.
Murder, not Voluntary Manslaughter.
Bottom line; absent the witness to show probable intent, Gov. might accept Voluntary Manslaughter.
Yes...there are 100 different what-ifs, but prof of intent is necessary.
Mens Rea