Why a power drill?

Why not the power drill? He had it there as part of the coverup for the murder he was planning all along. It was never revealed how he originally intended to kill her, but after the phone call, which led to the phone cord being used in an attempted strangling. Then he was conked out, he woke up shortly thereafter and went with the drill. Of course he could have just stabbed her with the drill...

He had that huge power drill to get into the safe in the wall. Instead of carrying that AND lugging around a knife or gun, he wanted to just go with one weapon? lol Two for one, tool and murder weapon in one! Plus that plug coming out gave us hope she might be saved. Why didn't she try to bash him with that lamp at least though?! Geez! =)

Why a drill? He was using it to crack a safe.

Cause Patrick Bateman loves the power drill

De Palma said he decided to use a drill as a murder instrument because "I do a lot of murder mysteries, and after a while you get tired of the usual instruments. You can use a knife, a rope, but now we have electrical instruments, which are truly terrifying." He added a drill was big enough to be seen by the character across a canyon. "It was not my intention to create a sexual image with the drill, although it could be construed that way.

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The scene was homage to an Alfred Hitchcock TV episode. No doubt that that DePalma knew that

Why? Because 3 or 4 decades later no one would remember what he used nor ask what he used.