After Michael shoots Solozzo he quickly turns and fires a shot into the front of McCluskey's neck. McCluskey gasps for air while tugging at his handkerchief to loosen it in an attempt to search for the wound. In that brief period of time between the shot in the neck and McCluskey crashing downward into the table Michael has this look of complete horror/disbelief but I think there was something underneath it all that made him choose against that final kill shot. He wanted McCluskey to look into his eyes and think about why as he went. Absolutely brutal scene. best mob hit ever portrayed in film in my opinion.