Torture is never justified. It is barbaric. I can't believe our leaders don't talk more about how widespread it is. It is embarasing to the whole race. I think the phrase is overused, but it truely is a crime against all humanity.
Also it is impractical:
The first problem is that you say "say he is Al Qeuda". What is he carrying a card? Let's say he was caught red handed. Next, we're assuming he knows how to disarm the bomb. Look, the pilots who flew the planes into the building didn't want to learn how to land them. Maybe he just doesn't know. Next, who's to say he's going to be truthful? What if he says: "just cut the blue wire". What do you do? Run out and cut the blue wire? Consult an expert?
No of course not. You evacuate the stadium. You make up some BS excuse that gets the fans out like, say, it's a drill or the power is going out and we are on backup generators, but they will only last a little while.
And after the incident is over? You give the man a trial. With a lawyer. Innocent until proven guilty. Full rights of any person in the US: right to not testify against yourself, right to legal council, right to trial by jury, right to not have cruel or unusual punishment inflicted.
That is called the law. We don't suspend the law every time a major crime is committed.
Certainly if there was a military force capable of invading the US and winning - actually destroying the US - then maybe there would be an argument for some special cases. This is not that. No more so then when McVeigh blew up the Federal building.
The greatest threat to the US right now is us, destroying our own rights in a, frankly, bizzare and misguided attempt to defeat a method used since biblical times: the use of violence against civilians to alter the political actions of a government.
Go read the patriot act, for example.