Info request

Does anyone know where I can get info on bullet penetration/mechanics?

A friend and I have a longstanding debate going about handgun calibers: He has a 9mm w/ hi-cap magazine, suitable for knocking cans off of fenceposts (with the assistance of a brisk tailwind); I prefer my 1991-style .45ACP for it's ability to knock down large buildings.

Anywhat, in this video (Warning: GRAPHIC) a man commits suicide in a police interrogation room with a 1991 style pistol, presumably in .45ACP. The bullet does not exit the skull as one would expect, and we're wondering why.

I've surmised that he may have had frangible ammo, or relatively light (185 grain) hollow points. Any opinions?