I wonder if he suffered some sort of head injury.
It is odd, but some people enter what is known as a "dissociative fugue" state where their character changes and they wander off, sometimes a great distance from home, often with amnesiac qualities.
http://[B][/B]neurophilosophy.wordp...ive-fugue-state-forgetting-ones-own-identity/
The wild spontaneity of the trip, and bad planning on his part (going to an unfamilliar, risky part of the world with nothing of value), may suggest something of this nature.
The difficult thing is that (apparently) nothing was noted at customs on the other end (assuming he ever got to Puerto Rico). Security is tight in that part of the world, and I am sure he would have interacted with border police there. They would have wondered why he arrived with few personal effects.
Puerto Rico is a U.S. territory, and I think the F.B.I. has jurisdiction there. I wonder if they have made the case public. If so, that may jog the memory of anyone who noticed him on a flight or at any airport.
BBM, The FBI has an office in San Juan, Puerto Rico. It's strange, I spend part of the year in Puerto Rico, but I have never heard anything about this case... Many of my in laws live on the Island, and I was talking to a couple of them the other day about this case...they have not heard anything about it either...Seems odd...JMO