Back in the 70s Dick Gregory was criss crossing the country giving lecture/testimonies on his knowledge and experiences of all sorts from the Kennedy and MLK hits, to the Patty Hearst deal "etc". Entertaining as well .. a GREAT and funny public speaker.
He said he got a lot of his information from the underground black back channels. Prostitutes, night porters, aware cats hanging out on the street just WATCHING and NOTICING 'things' etc. One night porter for the guy who did the RFK autopsy came across the actual report and passed it along to Gregory before the kill shot being point blank back of his head w/ powder burns was common knowledge. That kind of stuff.
Anyway he was contacted by a prostitute who had a regular who had no belly button. Totally flat .. nothing. Gregory even arranged for her to dope the guy unconscious so he could see for himself. At that time the surmising he and his people were doing was towards the guy being an off-worlder of some kind.