If one could do so safely (e.g. if one was with someone else who was also armed) would there be anything the police could find objectionable about giving first-aid to one's attacker? Certainly such first aid could be construed as 'altering a crime scene', but I would think saving the attacker's life to stand trial would outweigh that, would it not?
As to whether one should give first-aid, that would be a more complex question.
My advise is: Call 911 to show good faith. Worry about accomplices more than first aid. About one half of crimes involve more than one person. Do not get whacked while your attention is devoted to helping someone who moments before was trying to kill you.
If I just shot someone the last thing I would do is try to render first aid to the man. One moment you are “in fear for your life” and two minutes later you are deciding that this upstanding person is worthy of your first aid? What message is that going to send to a DA or a jury?
Yes, you should be ready to render aid to the perp if your safety is not put at risk by doing so.
I carry two standard GI pressure dressings in my vest, both for me if necessary; if not, I will use them on a perp if and only if I can secure the scene and the erp is not able to be a threat. The presence of the torn wrapper and the dressing bloodied and in place indicates I was not a man out to murder anyone, but that I called the police, asked for an ambulance, rendered basic 1st aid (or attempted to-the opened dressing would be on the ground near the perp when LEOs arrived). Also, I am an advanced life saver qualified Soldier, so I can demonstrate my ability to render aid as well.
The other question you present-SHOULD you render aid to a scumbag whom you just had cause to shoot; well, do not try to say that to a jury.....
God Bless
Molon Labe