The article states that the US military investigated it, so it's not an odd thing to say at all.

> In any case various international experts have stated that there is a viable case for war crimes to be made, based on the video evidence.

"Various international experts" can be counted on to pronounce any military activity whatsover by the United States as a war crime (while ignoring or even excusing the behavior of non-Western states), so that's of little use.