Duke nukem forever lady killer part 3?

lady killer part 3, i'm stuck on the bit, where there's the big duke statue and he's killed another duke on the floor, he has a gun with a laser pointing at him, you have to go to the button, to lower the platform's, i am not sure how to get past this bit. the chap at the top, say's you have to kill the duke, i've tried firing at him and it does nothing to him