They had the right to arrest him. They did not set out to kill him, and at no point was there any action that would ordinarily kill, so, whilst you may believe there is a case to answer, please stop referring to ‘capital crimes’ or ‘death penalty’. It’s blatant straw manning, to borrow a phrase. So, even from a purely impartial standpoint (which I am not, but go with it), there is no question of this being murder, in any way deliberate. So if you wish, call them violent, or perhaps guilty of manslaughter (not that I believe they are).
Furthermore, while I’m at it, leave halacha out of this. It isn’t relevant as far as this argument is concerned. Everybody seems to be forgetting that the people involved aren’t jewish, and as such are mechuyav to have a legal system, and that’s it. So simply talk about this in terms of Din, that is, the Law of the United States of America, and avoid making ill-advised, often misinformed comments about Beis Din and the like.