They have had the bomb at Quantico since last May.
It is encased in caulk in an effort to trap vapors that might alert any bomb-sniffing machines or dogs that did happen to be capable of identifying the explosive.and is totally non-metallic.
The only reason the plot was foiled:
"The suicide bomber dispatched by the Yemen branch of Al Qaeda last month to blow up a United States-bound airliner was actually an intelligence agent for Saudi Arabia who infiltrated the terrorist group and volunteered for the mission, American and foreign officials said Tuesday. " Source
The real reason they’re afraid of how much Snowden knows and will leak?