Yes your right it was James Chatters. For some reason I remembered him as two people instead of one guy with two areas of expertise. He was initially acting as a standard forensic anthropologist. The kind used for homicide investigations. He believed the skeleton was a European settler then quickly changed his mind.
I was able to recall that because I literally finished his book yesterday morning ("Ancient Encounters: Kennewick Man and the First Americans"). In that book, which was from 2001, he believed that the people who most physically resembled Kennewick Man were the Polynesians and the Ainu from Japan. He didn't say Kennewick Man was Ainu, or Polynesian, just that they shared the most physical characteristics.