When Abdulmutallab left Lagos airport late Christmas Eve, there was someone who'd already been worrying about him: his father.
Umaru Mtallab, who retired just this month as chairman of First Bank of Nigeria,, according to local reports, that his son's religious views had become "extreme." Mutallab was meeting with Nigerian police today.
In Britain, police quickly learned the suspect's last known home address and searched it, a pricy basement apartment in an upscale central London uilding.
But authorities are anxious to know much more.
Among the questions, said Peter Clarke, a former head of counterterrorism for the London police and CBS News consultant, are "Who did he know? Was he radicalized here; if so when, by whom?"
London's University College says Abdulmutallab studied mechanical engineering there until September 2008.
After that, his father believes he may have traveled to Yemen. U.S. authorities say extremism thrives in the Gulf state of Yemen, where al Qaeda has carved out a foothold. Abdulmutallab reportedly told investigators that's where he was trained by al Qaeda, and supplied with explosive chemicals.
Airport rules in Amsterdam state that even though Abdulmutallab had already been security-screened in Lagos, he would have been screened again before boarding his flight to Detroit.
But the airport has just a few body scanners to detect threats under a traveler's clothing; not everyone goes through one.
Abdulmutallab was barred from reentering Britain this year, though not for any known terror threat. He was said to have applied for a visa to continue his education - but the college claimed to be attending was fake.
But body scanners to detect guns and bombs can't screen for intent, and investigators are still trying to figure out how and why the son of a wealthy banker became a radical who wanted to destroy an airplane.