And what if that info is wrong? A gun can be small and if you take the time to look if the suspect realy has one, you can end up dead. This is so hard. And for a possible suicide bomber, it's even worse. A suicide bomber that know that they are suspected may use their device so stopping them for a search may not be an option. Evacuating bystanders may arise suspicion. Even risking killing an innocent by a "shoot first and be sorry later" policy may fail if the bomber have connected their device to a "Dead man's switch" that automatically detonates the device if they are taken down.
http://en.wikipedia.org/wiki/Dead_man%27s_switch
So far thou I have only seen they use of that trick in movies twice, in the Terminator 2 movie a guy had rigged a bomb to go off when he dies (he is dying at the time and hold out long enough for the cops to flee). Another example was in a movie I cannot remember the title of but the bad guy held out a bottle of nitroglycerin.
In any case, I served a few months in the swedish military as most swedish males does and I was instructed to when doing guard duty to fire at the legs of an attacker if possible. Leathal response was of cource permissable if neccessary thou. I was at the time equipped with a submachine gun so "hitting the legs" are a lot easier with a stream of bullets then a simple pistol can accomplish. I also had a baton of some reason but I cannot understand why, If I carry a SMG I will make sure the bad guy doesn't take it from me so I will hold on to it, thus I cannot use the baton. I would rather melee with the butt of the SMG then the baton, at least as long as I still got ammo in the gun.