Why did the FBI bow out? I can't answer that one. Probably it was a mistake on their part.
10 years later, we have an unsolved murder. There still remains:
- Possibility of a foreign involvement, as stated clearly by the ransom note author.
- Kidnapping for ransom conspiracy, also clearly stated by the author.
- There still has been no positive ID of the perp, either by handwriting or DNA.
- The meaning of SBTC is still unknown.
There have been other famous cases, the Lindbergh case, Leob and Leopold, the Unabomber, etc. etc. where the perp has been positively identified. As long as JBR's killer is not positively identified, you kinda have to be open to various ideas, the most apparent one being the botched kidnapping/murder idea, because thats what it seems to be.
It beats me, then, why the FBI isn't involved in what has presented itself as a botched kidnapping turned murder, with a foreign involvement. On the surface thats what it seems to be.
Call it a mirage if you want, thats still what it appears to be.