Captured after a bomb hidden in his underwear ignited but failed to explode, Abdulmutallab spoke freely and provided valuable intelligence, officials said. Federal agents repeatedly interviewed him or heard him speak to others. But when they read him his legal rights nearly 10 hours after the incident, he went silent…

The suspect spoke openly, said one official, talking in detail about what he’d done and the planning that went into the attack. Other counterterrorism officials speaking on condition of anonymity said it was during this questioning that he admitted he had been trained and instructed in the plot by al-Qaida operatives in Yemen…

Abdulmutallab’s interview ended when the suspect was given medication and the investigators decided it would be better to let the effects of the drugs wear off before pressing him further.

He would not be questioned again for more than five hours. By that point, officials said, FBI bosses in Washington had decided a new interrogation team was needed. They made that move in case the lack of a Miranda warning or the suspect’s medical condition at the time of the earlier conversations posed legal problems later on for prosecutors.