What mass and momentum did the bullets have?
I don’t think an RPG would have stopped that guy, initially! He, obviously suffered massive disintegration of his circulatory system. The brain wasn’t getting any blood! That’s what stopped him!
They are all pretty much the same. And no pistol round has “knockdown power”. If it did it would knock you backwards just as hard. Isaac Newton and all...
A 125JHP .357 Mag does seem to incapacitate faster than anything extant, but it doesn’t even knock anyone down. It’s a function of it’s velocity, bullet design and shocking power. But not everyone shoots it well.
The cop needs a .357 Magnum revolver and shooting lessons.
The .45, because shooting twice is just silly.