This may be the reason, via ABC News:
The senior U.S. official said there is concern about devices that could be implanted inside the body of a terrorist.This would be consistent with prior reports of this method of attack:
“We are concerned about surgically implanted devices,” they said. “These are guys who have developed the techniques to defeat our detection methods.”
The official also said authorities were stunned that the group broke “operational security” — meaning they talked likely knowing it would be picked up by intercepts.
The one aspect of the intelligence that officials appear to agree on is that Al Qaeda’s affiliate in Yemen is behind the plotting.How serious are they? This serious:
The group, Al Qaeda in the Arabian Peninsula, has tried to carry out several high-profile attacks in recent years. One was a man’s attempt to blow up a trans-Atlantic jet over Detroit on Dec. 25, 2009, using explosives sewn into his underwear. Months earlier, the group tried to kill the Saudi intelligence chief with a bomb surgically implanted in the attacker’s body.
American officials believe that both bombs were built by Ibrahim al-Asiri, one of the group’s leaders whom the Obama administration has been trying to kill as part of a campaign in Yemen using armed drones.
The  plan was engineered by AQAP’s ingenious chief bomb-maker Ibrahim al Asiri, who planted a bomb inside the rectum of his own brother. The operative gained an audience with the Saudi prince by pretending to defect and duly set off the bomb. But Nayef survived the attack.A recent attack in Afghanistan used this method:
Afghanistan’s spy chief, Asadullah Khalid, was taking no chances.There’s a long history of warnings about implanted bombs:
A man had crossed into Afghanistan from Pakistan with important information he said he would only deliver personally to Mr. Khalid, who had just taken over as the head of the National Directorate of Security.
Mr. Khalid’s aides took the visitor to an armored room in the basement of a safe house in Taimani, an upscale neighborhood in the capital city, for a security screening. They were no doubt mindful of what happened in September 2011 when a Taliban peace emissary was allowed to meet with a prominent Afghan peace envoy and then killed him with a bomb hidden in his turban.
Watching the man over closed-circuit television, they ordered him to strip naked, which he did. Satisfied, they let him get dressed and took him to see their boss upstairs.
Then he blew up. The suicide bomber killed only himself, but Mr. Khalid sustained severe abdominal wounds as well as injuries to his hands and arms.
Now, months after that attack, on Dec. 6, a spokesman for the National Directorate of Security, Shafiqullah Tahiri, confirmed that the attacker had hidden the bomb inside his rectum.
- July 7, 2011 – Bomb Implants Emerge as Airline Terror Threat
- April 30, 2012 – Officials Watch for Terrorists With Body Bombs on US-Bound Planes
- May 13, 2012 – Plastic explosives: Al-Qaeda-trained surgeons put the bomb in suicide bombers