Al Qaeda bombmaker Ibrahim al-Asiri was again the mastermind of the plot, according to U.S. and other intelligence sources. Asiri designed the bombs in the failed printer-bomb cargo plane plot of 2009 and earlier planted a bomb in the rectum of his brother, who died in a suicide attack on the Saudi intelligence chief. He also made Abdulmutallab's underwear bomb, which failed to detonate properly.
The FBI is currently examining the new bomb and is "exploiting" it for intelligence, Brennan said.
But according to former White House counter-terrorism advisor and current ABC News consultant Richard Clarke, the insider's escape from Yemen could put counter-terror operations at a disadvantage from here on out.
"You have to wonder if this plot was foiled by someone on the inside, whether or not that means that source is blown and therefore they no longer have someone on the insde and would not know about the next plot," Clarke said.
U.S. officials said Fahd al-Quso, the head of operations for AQAP, was killed over the weekend by a U.S. drone strike. Asiri, the bombmaker, is still at large, and is believed to be training other bombmakers and making other bombs, all aimed at U.S. aircraft.
AQAP has been described by numerous U.S. officials as a top security threat to the U.S. homeland, more so even than central al Qaeda formerly led by Osama bin Laden.