Let the legal authorities take charge and in this case the legal authorities according to governing law were the Kiev Ukrainians who sent in emergency workers to bag the dead while the pretend “Prime Minister” of Donetsk sent in looters to cover up the crime.
What would you do???
Treat any survivors.
Put out any fires.
If no survivors, photograph/document everything in situ.
Remove debris where necessary to provide access.
Recover/preserve remains.
I expect somewhere fairly early in this process local authorities would show up, and I would work/coördinate with/defer to them as much as possible. I expect in an active combat zone this would be problematic.
Be available to provide photos, sketches and any other data I can to the accident investigators when they finally show up.
Either way, we'd both do the best we can. We're Americans. We do that.