From the looks of it, the authorities in the UK were well on top of this situation beforehand and we simply gave them some extra intel so they felt confident about arresting the suspects.
More from Time:
Britain’s MI-5 intelligence service and Scotland Yard had been tracking the plot for several months, but only in the past two weeks had the plotters’ planning begun to crystallize, senior U.S. officials tell TIME. In the two or three days before the arrests, the cell was going operational, and authorities were pressed into action. MI5 and Scotland Yard agents tracked the plotters from the ground, while a knowledgeable American official says U.S. intelligence provided London authorities with intercepts of the group’s communications. Most of the suspects are second or third generation British citizens of Pakistani descent whose families hailed from war-torn Kashmir. U.S. officials believe the 29 members were divided into multiple cells and planned to break into small groups to board the nine planes.
And a little on the explosives, which seem to be a favorite among suicide bombers, including the ones on the London subway system:
FBI and Department of Homeland Security officials quickly alerted law enforcement agencies around the country to the peroxide-based liquid explosives the London plotters planned to bring aboard the American-bound planes. An alert the FBI and DHS sent out Thursday to state and local law enforcement agencies ÃƒÂ¢Ã¢â€šÂ¬Ã¢â‚¬? which is classified “For Official Use Only” and was obtained by TIME ÃƒÂ¢Ã¢â€šÂ¬Ã¢â‚¬? warns them that the peroxide-based explosives could also be employed in future attacks here.
The FBI-DHS report next warns law enforcement agencies about the two peroxide-based liquid explosive that could be used in a future attack against the U.S.–triacetone triperoxide (TATP) or hexamethylene triperoxide diamine (HMTD). The report describes how a terrorist would assemble bombs with these chemicals. Peroxide-based liquid explosives “are sensitive to heat, shock, and friction, can be initiated simply with fire or electrical charge, and can also be used to produce improvised detonators,” the report states. “For example, TATP or HMTD may be placed in a tube or syringe body in contact with a bare bulb filament, such as that obtained from inside a Christmas tree light bulb, to produce an explosion.” The report doesn’t mention anything about a terrorist assembling such a bomb on a plane, but it does warn that manufacturing such a device can be dangerous for the bombmaker. “Because of the instability of these substances,” the report notes, “spontaneous detonation can occur during the production process.”
Over the past ten years peroxide-based explosives have popped up in a number of terror operations, according to FBI-DHS report. “Terrorist have used peroxide-based explosive both as a main charge (weighing in excess of 20 pounds) and improvised detonators,” the joint assessment states. “TATP was popularized as a main charge explosive in suicide bombs used by Palestinian terrorist groups.”
More as it becomes available.