I think way back in the beginning there was some speculation as to whether or not the murderer might have spotted one or two of the victims online back when he was still living in Pennsylvania. I don't recall if logic suggested that would not have been likely. (Not recalling when each girl moved in.)
It's a little far-fetched, but it has crossed my mind to wonder if an obsession developed over a resident/s at 1122 King Rd. early on, before he ever crossed the country, to the point that it was one of the reasons he chose WSU. I recall he wanted to avoid a certain entrance exam type thing (I have no link so it's more an opinion), and WSU did not require the exam, so that could have helped him form his decision...... But it would really be something if a fixation on one or more of the victims motivated him to make his way to Moscow/Pullman in the first place.
I know there has been much speculation about how he found that house and those persons. Followed someone home from the Mad Greek? A connection at the pool party? Random prowling and peeping? The least likely way might be via the internet from his home base in PA (pinpointing an address for renters would seem trickier than maybe coming up with one for homeowners), but I have always wondered about the possibility. He bought the knife in PA......
Edit: punctuation