In the end of the movie Casino...?

Remember in the end of Casino when all the big bosses had a meeting in the back of the courthouse to have the people whacked, they shot the guy in Costa Rica, killed the Stone guy, and then there was a scene; A SCENE where there was a guy entering his car, and when he got in, some guy comes up and hits him with (what I think is) an axe. then he puts a plastic bag over his head as it fills with blood. MY QUESTION is what did that guy do to the driver, to kill him like that? what was that that he hit him with? (I guess the scene happened so fast, that I didn�t notice too much how severe that kill was.)