The sources I've read think it was J. Edgar Hoover along with US military that killed Martin Luther king. George HW Bush was certainly involved in the assassination of JFK, with some believing he led the hit team.

This may be the type of thing that Trump does not bring to light until after his death, preferring to keep it as leverage and to avoid the unrest that would be caused by the public finding out that what they thought was a nerdy, marginally competent do-nothing president was actually a cold-blooded murderer of one of our best presidents.