General rule is that first murder is closest to home, familiar hunting grounds as it were, but there's really not much close to Washougal and 14, but lots of woods for watching. IF the killer were close to Washougal, then it might make sense. I'm not sold on that one being linked; need to know more.
Silverton,OR has a population of 651 people, but it's only 25 minutes from Salem. Moscow is a leap from there, not just in distance, but in roads. 12 and 95 are a lot of not much. IF these are linked, then this is someone who really knows the PNW or has relocated to somewhere closer to Moscow. If the killer were traveling eastbound through WA, here is where you can look at the roads in and out.
https://wsdot.com/travel/real-time/mountainpasses/white