TODAY | May 10, 2012
>> is learning more about the underwear bomb taken out of yemen by a double agent in that foiled al qaeda plot to bring down a u.s.-bound passenger plane. officials say the device bears the hallmarks of the terror network's master bombmaker. nbc's chief foreign correspondent, richard engel , is here with more on that.
>> some consider this bombmaker to be right now the most dangerous terrorist in the world. he's already tried to attack u.s. aviation at least three times. and there are no signs that he has any intention of stopping.
>> reporter: ibrahim al asiri isn't an ideologue or firebrand cleric. instead, he's a skilled, practical and inventive bombmaker. he's good. he learns. and that's what makes him so dangerous.
>> he's not going to go away. the u.s. knows it. and so we need to continue to aggressively identify his location and put him out of business.
>> reporter: around 30 years old, born in saudi arabia , once arrested in saudi arabia , he seems to have only one goal. according to u.s. officials, it is to build a completely metal-free bomb. he studies airport security systems and wants to beat them. al asiri seems to like what he does. security experts say he enjoys playing master terrorist, and he's getting better. al asiri's signature is easy to spot. he makes small powder bombs made of petn, a type of plastic explosive. the lack of metal means they're not powerful. there's no shrapnel. but they don't set off metal detectors . he also makes them into underwear so they're unlikely to be found in a basic airport pat-down. al asiri apparently knows he's at the top of the u.s. target list and moving up. he's practical about that possibility, too.
>> what's particularly troubling is that he's also looking to teach others his capability and his skills so that in the event that he is taken off the scene, there will be others who can continue to do his type of bombmaking.
>> reporter: also different, u.s. officials say, is al asiri's level of dedication. he even dispatched his own brother as a suicide bomber wearing one of his bombs either as a suppository for clenched between his legs. on christmas day 2009 , al asiri made the bomb worn by a nigerian on a u.s.-bound plane to detroit. the bomb made it on the flight but didn't fully detonate. he tried again according to security officials mailing a petn bomb to the united states stuffed in an ink cartridge . it, too, was undetected, only found because of a tip. and then last month, u.s. officials say, al asiri wanted to sneak an improved underwear bomb on a u.s.-bound flight for the anniversary of osama bin laden 's death a year ago. but the plot was disrupted and the bomb seized. yemen is emerging as one of al qaeda 's leading sanctuaries, but the yemeni government is cooperating with u.s. officials in looking for this bombmaker.