Who is Jim Forrester from Dead in the Water: A Novel and what is their importance?

Jim Forrester is a magazine writer who claims he was in the Canary Islands to do a travel piece for the New Yorker magazine and was asked to go to St. Marks to write a piece on Allison Manning. It also turns out that Forrester met the Mannings in the Canary Islands. In fact, Forrester quickly agrees to testify in Allison's trial. Forrester's story changes every time Stone questions him, but it is always in Allison's favor. In the end, however, these questions cause Stone to check into Forrester's story. Stone eventually establishes that Forrester is really Paul Manning, disguising himself by having lost a large amount of weight.