As always, screenshots are not enough evidence to get someone punished, there are very few scenarios in which screenshots can be enough to cover things up. For these types of situations, use a video recorder, to make it easier to capture the situation and present it here. They will be monitored, but this is not something to punish them for, might be possible if you were following them (even though you did not attack them, following can be a valid reason to be killed).
Good luck next time, until then, this will be dismissed.