It's damn hard to stop people from doing harm if they're willing to kill themselves... but that's no real answer.
Here's one of many stories.
[poor Nigeria, their rep was bad enough with simply internet scams!]
[update:] Maybe it's this, from David Brooks' column in the New York Times.
At some point, it’s worth pointing out that it wasn’t the centralized system that stopped terrorism in this instance. As with the shoe bomber, as with the plane that went down in Shanksville, Pa., it was decentralized citizen action. The plot was foiled by nonexpert civilians who had the advantage of the concrete information right in front of them — and the spirit to take the initiative.
For better or worse, over the past 50 years we have concentrated authority in centralized agencies and reduced the role of decentralized citizen action.