Which was it? Was he surrendering with his hands raised or running away? Both have been reported by the media, but the truth is we really don't know.
One hypothetical situation where the use of deadly force would be reasonable against an unarmed man with his hands raised would be after a struggle for the officers weapon and with a suspect in close quarters, but still approaching and refusing orders. If that's actually what happened I would not fault the officer for opening fire.
Bookmarks