Heather Went On Killing Spree
The 2nd letter from Heather, in so many words, confirms the theory that she has gone on a killing spree across the US (Denton County, TX, Meeman State Park, TN, Indian Head, MD). She writes that she is visiting the obelisk (presumably Concord Point Lighthouse) everyday waiting for JWJ to meet her there. She also tells JWJ that she is staying at a motel nearby and using an internet cafe nearby.
Originally thought that the last victim at Indian Head, MD was that of the internet cafe barista. But Indian Head, MD is 100 miles from Concord Point Lighthouse. I do not believe Heather would drive 100 miles to use an internet cafe when she describes It as a "nearby cafe". So the body of the man in Indian Head and the body of the man in Meeman State Park are still a mystery to us.