Head blown apart by a self inflicted shot to the temple? Which gun?

The WP article by David Maraniss says the cops found one gun by the killer-- where did the other one go? Where was it found? Which gun was used by the killer to blow his head apart? How can the head be mangled by a shot to the temple? Here's another blog that indicates a scene from a movie that Cho presumably modelled his performance on...

"Cho pointing a gun at his own head quoting Robert de Niro’s famous scene in “Taxi Driver,” in which he follows a slaughter of perceived villains with a suicidal blowing of his head apart, just as Cho did. " [+]