"You're not Jigsaw bitch!"
Lol

The murderer of Gwyneth Paltrow's character, Paula Bell, was Jigsaw!
And before he murders her the killer and victim have a brief interaction in Andy's office.

Hitchcock would call the plot device of the rapist the "McGuffin."
Not quite. In this case, the rapist subplot was a "red herring." A "McGuffin" is something entirely different. It's a plot device to set the story in motion, but in the end it does't really affect anything and is all but forgotten by the time the climax.

Hitchcock would call the plot device of the rapist the "McGuffin."

The rapist/killer was a maintenance man who worked for Andy's school and who saw the girls he wanted to attack in Andy's office (as girls who had appointments with Andy at the college). The man is shown literally bumping into Gwyneth Paltrow on her way out of Andy's office after the one appointment that appears in the movie.
It was significant because the proximity of the girls to Andy gave the police detective a reason to ask Andy for a sperm sample to clear him as a suspect.
This was significant because it resulted in a lab test which showed Andy as being sterile.
This was significant because Andy told the police detective that Tracy had been pregnant when her ovarian cyst erupted and her life was in danger.
This was significant because it caused Tracy's and Jed's insurance scheme to fall apart.
The rapist/killer was a plot device, in other words.