Suppose the crotch bomber had had anthrax secreted there.
We are in serious trouble and the administration has leaders in the fight who think the answer is political correctness, i.e. ‘man made disasters’ caused by ‘lone’ partisans.
Biologicals are too technical. These knuckleheads have been playing with chemicals for years. What they are finding is that you need to know what you are doing, and have the facilities and technology to not kill yourself while mixing up this stuff. It is a lot more complicated than it appears. As pointed out by rbg81, it is likely they dropped the chemical attack because their tests did not go well.
That is the reason you are seeing more creative ways to secret explosives on planes. The underwear bomber is a prime example. Look for them to shotgun security to get a few through to carry out their mission.