I feel they know, and i hope no one can run away from own DNA. I think it is not anyone "Moscow-local", but "Idaho-local", and even a student, he could be. Could be a "neighbor" from WA, MT or OR, as Idaho panhandle is pretty narrow.
During the holidays, people can visit relatives, old grandparents, for example, and then quietly leave one morning, not telling their old folks. People travel to Canada, more so, to Mexico or Dominican Republic, away from cold. Alaska and some crab ship is not impossible. I found several new touristy destinations where one would stick out, but no one would pay attention at the same time, as these places thrive on tourism.
A lot depends on whether the person has a passport, or an enhanced driver's license. Having a license only limits one's possibilities.
Another question is, where in the world the family has relatives?
A question I'd consider. Cuba. It is super easy to get there from Canada, and not expensive to live there. Do you know how is their attitude to US passport now?
I just hope that no country needs to accommodate someone else's knife murderer of women.