Admittedly this is the first I've heard of this but it strikes me as people trying to cash-in on the "Jesus' life and the mysteries that surround it" craze (Priory of Sion, Gospel of Judas etc.) that has sprung up since that damn DiVinci Code came out.
I'd just like to put in that Truman was an idiot. Not completely his fault though, as FDR never talked to him before he died, so Truman had no idea what he was doing. I'll add more detail after I re-research it a little bit.