I completely support the cop in this case. He might very well have saved the life of the girl being attacked. It's instructive that the headlines all read "Cop kills black teenager," which is much more inflammatory than "Cop saves woman from knife attack," which is what actually happened.
Nonetheless, this was a troubled 16-year old foster kid, probably typical of hundreds of thousands of kids in this country who personify the socialist state. She was not quite at an age where her life could be considered her responsibility. She was the product of a lot of failed institutional programs. I am very saddened by that.
It's too bad we can't kill the programs that created her as easily as she was killed.