(psssstttt LBJ did it) ;0)
He is a writer, but the real brains of the idea is Howard Donahue, a ballistics expert who was one of seven shooters in Maryland in 1969 to recreate Oswald's "impossible" feat of 2 hits and 3 shots in 6 seconds. (Later, Posner showed that it was really 10 seconds, and that the Zapruder camera was not correctly calibrated). Donahue got THREE hits in 6.6 seconds with the Mann. Carcano rifle. He said the head wound was not consistent with a M-C from behind, but with a M-16/AR-15 from behind. He produced a photo of Hickey, riding in the trail car, right behind JFK, with such a rifle. It got more mysterous after he contacted Hickey. Basically, Hickey filed a report that said nothing, and no one would let anyone talk to him again.