Do you think that LBJ had anything to do with the murder? He might have thought that he needed to carry Illinois to win re-election in 1968.
LBJ didn't run for re-election in 1968. Nixon defeated VP Hubert Humphrey that year.
Something really upset LBJ not to run in 1968. I remember the announcement, and it looked he had seen a ghost.
It is possible somebody found some skeletons in LBJ's closet and were going to use them on him if he ran. He was one very scared person when he made the announcement he would not run (IMHO).