One source told CNN that the device was recovered around April 20, more than a week before the first anniversary of the killing of Osama bin Laden, and was then handed over to the United States for forensic analysis.
The agent was sent to Yemen "months and months" ago, when Saudi sources in Yemen reported indications that al Qaeda in the Arabian Peninsula, or AQAP, might be again preparing a plot against U.S. aviation, one source said.
These were the first indications "that al Qaeda might be trying again," according to one source, after the Christmas Day 2009 underwear bomb plot and the laser-printer bombs dispatched from Yemen in October 2010.
The whole operation was personally overseen by Prince Mohammed bin Nayef, the head of Saudi counterterrorism, one source said.
Initial reports had not revealed the extent of Saudi involvement.
At one point, the Saudi agent reported that a device was being built, and the Saudis then informed the United States, according to one of the latest sources, who spoke to CNN on condition of anonymity, citing the sensitivity of the information.
The agent then received training on the device from AQAP instructors.
According to one source the device contained PETN explosive, the same explosive used in previous attacks by AQAP's master bomb-maker Ibrahim al Asiri.
Describing the bomb, one source said it was smaller than previous bombs made by al-Asiri.
The other said it contained an amount of explosive similar to that hidden inside laser printers that were sent from Yemen in October 2010 . The printer devices contained 300 to 400 grams of explosive and had a larger amount of high explosive than carried in the Christmas Day flight from Amsterdam to Detroit.
One source told CNN the device was designed to be worn in clothing. There has been no confirmation from other sources of that detail. The source said the device was "more advanced" than the underwear device, as al-Asiri was trying to rectify past mistakes. The device in 2009 failed to detonate, apparently because the detonation charge failed to set off the PETN explosives.
The source added that AQAP bomb-makers apparently believed that in the case of the Christmas Day plot they had got the initiator mechanism wrong, and that the mistake in that case was to mix acids slowly in an effort to begin the detonation.
Homeland Security Secretary Janet Napolitano told reporters Tuesday that the device is "similar to the underwear bomber of 2009, but an evolution to that."
Saudi intelligence had hoped that their agent would be able to get information about al-Asiri's whereabouts, but the agent did not meet al-Asiri, one source said.
One source cautioned: "Even if al-Asiri is eventually killed, we should not celebrate, because he has trained many people."
It is still unclear how the device left Yemen. One Arab source familiar with the investigation said he assumed it had been carried on a plane, which would raise troubling questions about airport security in the capital, Sanaa. But another hinted that it had been carried overland, in the possession of the Saudi mole.
One source said Saudi counterterrorism officials were upset that details of the operation had emerged in the United States because they had a network of agents inside AQAP who could be compromised by leaks from Washington.