John Pistole told the Aspen Security Forum: "The bomber had had the device with him for over two weeks."
Mr Pistole was then asked whether the bomb had become 'damp', to which he replied: "Let's say it was degraded."
During his trial, Abdulmutallab said the bomb in his underwear was a 'blessed weapon' to avenge poorly treated Muslims around the world.
After the bomb failed to detonate, passengers pounced on Abdulmutallab and forced him to the front of Northwest Airlines Flight 253 where he was held until the plane landed minutes later.
In 2009, months before the attack, he travelled to Yemen to see Anwar al-Awlaki, an American-born cleric and one of the best-known al Qaeda figures, according to the government.
He told investigators that his mission was approved after a three-day visit with his mentor.
Al-Awlaki and the bomb maker were killed in a U.S. drone strike in Yemen in 2011, just days before Abdulmutallab's trial. At the time, President Barack Obama publicly blamed al-Awlaki for the terrorism plot.
- Daily Mail