Sirhan Sirhan claimed he was mind controlled by the CIA. He detailed a number of the mind control methods used, but was written off as a crazy nut-case. However FOIA documents later revealed that the CIA's MK Ultra experiments were using techniques almost identical to what Sirhan Sirhan detailed.... creepy.

The British hypnotist Derren Brown had a TV show called "The Experiments" where he tested various mind-control techniques. In the show, he claims he was able to hypnotize a person enough where he could use an activation word which would cause the person to assassinate a specific target. On the show, the "assassin" attempted to shoot Stephen Fry on stage (with blanks) in front of an audience.

Whether or not Brown's techniques worked for real or not is something you would need to decide for yourself by watching the show, however I've heard interviews with Brown since, and apparently the person hypnotized as an assassin has experienced PTSD from the show.

TLDR; The CIA had MK Ultra and maybe used it on Sirhan Sirhan and Derren Brown used the same tricks on a guy on TV.