Clown Killer Into Phone Sex

Hi there, and thanks in advance for anyone's time taken for answering my question.

I saw a movie as a kid, maybe fifteen or sixteen years ago, and I can't remember anything about it other than this one scene in the movie. The story is that these cops are trying to catch a serial killer who dresses as a clown but is heavy into phone sex. They dispatch an attractive young woman to be the bait in a sting operation. They arrange it so that the killer is enticed into calling her from a phone booth so they can catch him, but something goes awry, and it cuts to this intensely creepy scene where the man slowly sneaks in through the woman's open window, comes up behind her and kills her while still on the phone.

I may even be fuzzy on those details, but could anyone help? Thanks a bunch!