I think the question is deliberately naive and baiting.
The accusation of “war crimes” requires an actual, full investigation (and trial) to be completely valid and/or meaningful.
Instead, it’s thrown out any time an act of war appears to be particularly unfair or evil, often without full context or detail.
If you were accused of a war crime, who would you want involved?
Accuser, defender, and as close as possible to a neutral host/judge/jury?
It seems that’s the best we can do.