There was an episode of Magnum PI which I remember because it spoke to this issue.
The plot was that Magnum's friend who flew the helicopter was brainwashed while a POW in "Nam" and given a post hypnotic suggestion...it would cause him to arm his helicopter and shoot up a meeting room with VIPs where sitting. Of course Magnum is able to stop him at the last moment..somehow.
Doesn't matter how possible all the above is...but what happens next is that Magnum is able to track down the bad guy who gave the hypnosis to Mag's friend and many other POWs.....some who had already acted on the suggest and killed folks.
Magnum confronted him out in the wilds of Hawaii someplace, had a gun pointed at him and the bad guy says something to the effect...there is no proof I did anything so I will not be convicted and you Americans are so crippled by following the law that you cannot shoot me and I can continue eliminating your people.
The final scene showed the pistol, a 1911, Magnum was pointing at the bad guy and I don't remember if it faded and we just heard the gun blast or if we saw the muzzle flash too..
In any case, the bad guy was dead out in the swamp some place....
In some cases, that one to me, principal outweighs the Law.