You geezers are letting emotion get in the way of common sense. Don't get me wrong, if I saw someone attacking my kids, I would kill the scumbag !! without doubt.
But what you have here is your typical courtroom conundrum... plus our rather sensible legal system - which, as it happens, is there to protect innocnents on boths sides of a row.
There's nothing more complex than a crime scene, and once battle weary barristers get involved, they could make a sausage look like a pig suicide !!
The point being, we don't hang people these days in case evidence was wrong, or tampered with, or one barister was better than the other, or the police cocked up etc etc.... so basically it's too dangerous to hang a crim, in case they weren't for some reason?