They did it their own way

"Yes, I´m a programmed killer."

Jesse Ventura's Conspiracy Theory asked: Is there a government´s plot to turn ordinary citizens into programmed killers?
See this doc. Manchurian Candidate & MK ULTRA.
In one episode, if you remember, Jesse Ventura claims to have uncovered a CIA conspiracy to create real-life Manchurian Candidates, brainwashed assassins who kill under orders but without any conscious intent.

This is an interesting case, because we know for a fact that the CIA at least attempted to do this in the 1970s as part of project MK-ULTRA.
Perhaps It's also true that many people with psychiatric issues can perform complex actions (like committing murder) while in a fugue or dissociative state.
And furthermore, the act of committing murder could certainly create traumatic amnesia, such that the killer truly does not remember having killed someone.

And finally we have the entirely plausible theory that these killer are lying in order to get a reduced sentence.

Faced with all these possibilities, and with the understanding of humanity as a vast and complex population, `CIA mind programming´ honestly seems like the least likely explanation, but the Verunture´s evidence is hard.

Drawing: the killer of
Prime Minister Olof Palme.

The fundamental problem is that both lying and a psychiatric disorder are both far more likely explanations. Or both, since, as they reported this method, a killer programmed persona´s mind will be broken by torture, during the training-period.
Between those two perfectly understandable causes, how much territory is left for "secret CIA programming"?
Enough left, I think so.

Probably the most damning case against sleeper assassins is that if it really worked, people would be using it. Imagine being able to kidnap a trusted advisor, program him to become a sleeper assassin, then return him to his native country to kill his leader. Is there any assassination targets left in the world, that works like a proof enough that it's not a real thing.