Umar Abdulmutallab, nigerianeren som forsøkte å sprenge seg selv og medpassasjerene i lufta over Detroit 1. juledag 2011, mislykkes fordi han ikke hadde skiftet underbukse på to uker.

Det at han gikk med den samme i så lang tid gjorde at bombematerialet og lunten ble ødelagt av skitt, opplystte amerikanske tjenestemenn torsdag.

John Pistole, the head of the Transportation Security Administration (TSA), said on Thursday that the bomb did not detonate because Abdulmutallab had been wearing the same underwear for more than two weeks.

«He had it with him for over two weeks,» Mr Pistole said at the Aspen Security Forum.

Asked by his interviewer whether the bomb’s fuse had become «damp» from two weeks of wear, Mr Pistole said: «Let’s say it was degraded. We’re getting kind of personal now.»

Mr Pistole, who oversees the agency tasked with protecting America’s civilian air traffic from terrorism, agreed with the interviewer when she remarked: «Thank goodness for bad hygiene, right?»

Abdulmutallab, now 27, was sentenced to life in prison for attempted use of a weapon of mass destruction and attempted murder.

His bomb was made by al-Qaeda in the Arabian Peninsula (AQAP), the terror group’s deadly Yemeni offshoot.

Western intelligence remains concerned that AQAP will try to find a European or American jihadist trained in Syria and supply them with a sophisticated bomb that can slip undetected onto a plane.