Complex sentence: Rather than being relieved of duty after the assassination, Kellerman, along with agent William Greer, forcibly removed JFK's body from Parkland and maintained custody of it during the autopsy at Bethesda and up until until preparation for burial.
Split into simpler sentences: Rather than being relieved of duty after the assassination, Kellerman, along with agent William Greer, were in a position to controll the evidence. They forcibly removed JFK's body from Parkland and maintained custody of it during the autopsy at Bethesda and up until until preparation for burial.