I haven’t looked at any of the photos/videos (nor do I intend to-I’m beyond caring) but just based on my recent firearms training, you don’t let someone with a knife get within 21 feet of you. You wouldn’t have time to neutralize the threat with a gun if you do.
That’s right, The video i saw looked like the girl was going to stab someone else when she was shot. So the cop was saving another life.