Umar Farouk Abdulmutallab spent time in Yemen on two occasions before the attempted Christmas Day attack on a Detroit-bound Northwest Airlines flight.
Yemeni officials said Abdulmutallab's student visa for Yemen, where he studied Arabic at a local language institute, was valid from Aug. 4 to Sept. 21.
After his visa expired, the 23-year-old stayed on in Yemen until the first week in December, they said, but his whereabouts in the country was unknown. The officials said Abdulmutallab left Yemen on Dec. 7 on a flight to Ethiopia and then continued on a few days later to Ghana. In Ghana, he is believed to have purchased the ticket for the flight from Lagos to Detroit that he is accused of trying to bring down.
Investigators told CBS News that they suspect Abdulmutallab, who is currently in a U.S. prison facility, brought the explosive compound, PETN, with him from Yemen.
Abdulmutallab has been assigned a public defender and has not been spoken to investigators in recent days - a change from the talkative approach he took with authorities immediately following his arrest.
In those discussions, Abdulmutallab indicated he had trained with al Qaeda operatives in Yemen and had a face-to-face meeting with radical imam Anwar al Awlaki, who has also been linked to alleged Fort Hood shooter Nidal Hasan.
Investigators told CBS News that Abdulmutallab furnished names of associates but most of those names have turned out to be aliases.
Yemeni official said that Yemen's airport authorities and passport control should have prevented Abdulmutallab from departing. The officials spoke on condition of anonymity because they were not authorized to discuss the case with the media, pending the outcome of an investigation.
The probe will look into why the Nigerian wasn't detained, questioned and prohibited from leaving the country, they said.
Administrators at the school where Abdulmutallab studied believed he had left the country in September, they said.
"We arranged a taxi to take him to the airport on Sept. 21 and we said goodbye," school director Muhammad al-Anisi told The Associated Press. "Our responsibility toward him ended that day."
Al-Anisi said no one from the airport security or immigration had subsequently contacted the school to ask about the student's whereabouts.
Yemen has confirmed Abdulmutallab spent two periods in Yemen, from 2004-2005 and from August to December of this year. He was enrolled at the school during both periods to study Arabic.
Al Qaeda in the Arabian Peninsula, an offshoot of Osama bin Laden's group, claimed it was behind the attempt to bomb the Northwest airliner.
More coverage from CBSNews.com:
Obama to Get Report on Abdulmutallab
Bomb Plot Exposed Lack of Intel "Urgency"
Official: We Knew Al Qaeda Planned "Christmas Surprise"
U.S. Intel Lapses Helped Abdulmutallab
Friend Says Abdulmutallab Was Not Extremist in London
Yemen, North Africa: Terrorism's New Home
Yemen Raids Al Qaeda Hide-Out; 1 Arrested
Opposition Grows to Transferring Gitmo Detainees to Yemen
Dick Cheney: Obama Stance "Makes Us Less Safe"
Democrats Say GOP Playing Politics on Bombing Attempt
Obama: "Systemic Failure" Allowed Attack
Roommate: Abdulmutallab Shunned Women
Abdulmutallab's Missing Months in Yemen
TSA Still Vexed by Explosives Screening
Tracing Bomb Suspect's Journey to Detroit