Wouldn’t have mattered unless someone got a head shot on the perp, since he supposedly had a vest on.
I haven't seen that reported. In any case, a vest doesn't make you Superman -- a good hit or two or three will take most people off their feet and knock the wind out of them for at least a little while, An incapacitated spree killer might not have the frisson of a dead one, but it stops the spree.