"Just Watch Me"
UK and USA commentards may wish to read up on the October Crisis in Canada in 1970. I don't think the invoking of the War Measures Act or the arrest of hundreds of political activists had anything to do with the resolution of this killing and kidnapping.
Did all the surveillance and invasion of privacy prevent this killing in France? It seems that it helped to the degree that the authorities were quickly able to identify these people and knew where to look and find most of them. But prevent it?
I think the real answer is twofold:
Bite the bullet in the Mid-East. Why is it only now that the oil wells/refineries financing ISIS are being attacked (bombed -- by the Russians)? I know all the good reasons against boots on the ground. How has that worked so far?
Deal with the disaffected locally. In Canada the guy who attacked the parliament buildings was a troubled soul who asked for help while in court in Vancouver. He got none.