Wouldn't most rapists want them 'as is'?
The sun shone, having no alternative, on the nothing new. Samuel Beckett
I don't think he meant for them to be laundered. He probably just threw them in the chute on his way to his room. I'm sure he realized they'd be discarded or thrown in the rag bin, as Mary Pilant said she did.
shareBiegler, I think, suggested that he threw the panties in the laundry as a quick cover up
. The panties were evidence. He didn’t want to toss them in the trash or something where they could be found by detectives. He also didn’t get a chance to burn or bury the panties.
So he tossed them in the laundry, a place where the panties wouldnt be noticed. The panties would presumably be lost in the midst of other like-minded clothing.