No telling what caliber he had. Bullets of all calibers do funny things when they hit glass. Even rifle bullets can have a hard time with glass deflecting them and redirecting their energy.
That said, I think penetration is the most important quality in a defensive handgun round (aside from accuracy). Expansion and bullet diameter are a very good things, but only if they do not compromise penetration. That's one reason I will not use HPs in any caliber under 9mm or .38 Special +P.