You leave witnesses because a) you know nobody will prosecute the IDF, and b) it allows people like you to question whether the clear mass murder was a mass murder.
FWIW, to me what it looks like based on the very limited information we have, is initially the soldiers thought (for whatever reason, possibly unreasonably) the vehicle was an acceptable target. At some point it becomes clear it wasn't and they have an "oh shit" moment and engage in a cover up after the fact.
If this is actually what happened (obviously,very big if), whether or not a war crime was comitted would come down to what the soldiers knew when they attacked the vehicle (and what would have been reasonable for them to have known at that time) since war crimes do have an intent element.
Which to be very clear, even with all the above, its very plausible a war crime was comitted. But i'm not sure its certain based on the publicly available information.
