Knock yourself out. Personally I seriously doubt I will be rendering assistance to anyone who just attacked me and was forced to shoot.
There are good reasons why approaching an individual who APPEARS to be incapacitated could be unwise. And why calling 911, in stead, as soon as you can would be best for your own physical safety. There'd also be a record of your attempt to get medical help as soon as possible.
Somewhere out there, I know there's a prosecutor who'd say, "Aha, he carried first aid for the person he planned in advance to shoot".