Maybe he didn't arrest her or cuff her because he wasn't a cop. Or maybe he was off duty because he isn't dressed like a cop.
MAYBE (and this is what I think happened) he offered to give the young lady a ride home and she refused.
Then he told her he would have to search her for drugs (threatening her with arrest if she didn't just go with him).
He chased her down, pinned her on the bench, and searched her purse. Then he let her up. He probably offered again to give her a ride, and she refused and tried to escape. He catches her, then after a few seconds, slams her to the ground again.
The other on duty cops come out, and he tells them she attacked him. She gets up and tries to tell them what happened (and what a creep he is) and he says she is lying.
That's when she charges him with the knife.
She gets shot, no audio for us to hear, and no one is the wiser (at least of the general public).
Heh, well I do not know if he was offering her a ride while they were over there by the seats.
Watching it in full screen it appears to me that he has his gun directly to her head at that time.
So I cannot imagine at all what is being said, but yeah, sound is needed here big time.
Whoa!!!
Freakin plausible!
Makes more sense than their explanation.