By definition, clandestine organizations have a need to keep their operations secret. So what better way than to compel an unwitting subject to act as an agent, commit unscrupulous acts and have no memory after the fact?

The CIA spent years and funneled massive amounts of resources into gaining this ability. CIA internal documents suggest that they succeeded. And if the agency developed the capability of taking a man or woman off the street and turning him or her into a remorseless killer or bloodthirsty saboteur, did they use it?

Some theorize that Sirhan Sirhan, who killed Robert F. Kennedy; Mark David Chapman, who murdered John Lennon; and James Earl Ray, who assassinated Martin Luther King, Jr., are all examples of the CIA, or another entity, employing this tactic. These agents, if they exist, are known as "Manchurian candidates," after the movie of the same name.