Actually, there may not be a culprit. There have been 10 feet found washed ashore in the Pacific Northwest since August, 2007 and several have proven to have been disarticulated from bodies due to decay. Foul play hasn't been ruled out but as of now there is no evidence of it. There is even one theory that these may be from submerged victims of the giant Indonesia tsunami since the shoes seem to pre-date that incident. Here is a wikipedia article about it.