Throughout the 70's and 80's, groups such as Red Army Faction, Baarder-Meinhof, Action Directe, IRA, Red Brigade, and many others operated and perpetrated bombings throughout Europe, the U.K. and Northern Ireland, many were killed, but a number were captured, they were successfully put on trial and sentenced accordingly, some are still languishing behind bars, such as "Carlos the Jackal"", while others have done their time and been released back into society, as in many of the former IRA.
The defining thing was they were tried and convicted in courts of law, for the crimes they committed, they were not detained without trial, tortured, humiliated, nor were they barred from legal council.
Catch them, try them, convict them.
That is the way it must be done, by detaining them without trial, they become living martyrs to the cause, and more and more young men and women pick up arms and perpetrate atrocities in their names, or in the name of, or for those in custody.