U.S. officials offered the first clues Tuesday about what they believe made a newly discovered al-Qaida bomb more reliable than one that failed to detonate aboard a jetliner on Christmas 2009.
The new device, seized during a covert CIA operation recently, contained the chemical lead azide, a compound that was not used in the Christmas bomb, the officials said.
They spoke on condition of anonymity because they were not authorized to discuss the information publicly.
Lead azide is an explosive that is often used as a detonator. A bomber would ignite the lead azide, which would trigger another more powerful explosive.
Terrorist training manuals have advocated the use of lead azide as a detonator. And it was a key component in a plot that nearly took down cargo jets in 2010.
In that plot, al-Qaida hid bombs in printer cartridges, allowing them to slip past cargo handlers and airport screeners.
That plot ultimately failed only because the United States and other intelligence agencies were tipped off to the bombs. Investigators determined that the cargo bombs would have worked.