In many cases, I would think it should suffice to say that one believed the person might pose a threat. Perhaps the 'attacker pretends to be bleeding to death so as to ambush the intended victim' thing happens more often in movies than real life, but unless one has assistance to secure the scene one could very reasonably argue that getting close enough to render first aid would be dangerous.
Your point is well taken.
However, having the means and intent to render aid is my point. It will add mileage to the idea that you only wanted to stop the perp.
I would practice this procedure as well as anything else-that way when/if such a thing happens, you will do what you practiced; rational thought WILL escape you for a while.
Dropping even a unopened dressing would be evidence found, that could not disregarded and would indicate more than simple words.
Your attorney will prompt you for all kinds of things, everything you can provide will help the PA decide whether you were justified or not-the sole test of the case.
God Bless
Molon Labe