A couple of comments on the shoot in the kneecap, crotch, etc. suggestions.

I will not re-hash a shoot-to-kill vs. shoot-to-disable argument here, but, there is one crucial reason why if you have decided to shoot you do not try to shoot for any part of the body except for the center of mass unless you are extremely good.

In situations like the one described by the OP where you fear for your life you will be in flight or fight mode. Adrenaline will be pumping and you will most likely lose fine motor skills ( i.e. ability to acutely aim for a small target). Hence, the likelihood that you will hit an arm, crotch, or other specific body part is very unlikely unless you are highly-trained. This is why you aim for center of mass of your target. If you aim center of mass you have the highest likelihood to hit your target and eliminate the threat it poses.

So, if you have decided to shoot, this is where you aim.