Sen. Carl LevinCarl Milton LevinSen. Gillibrand, eyeing 2020 bid, rankles some Democrats The Hill's 12:30 Report Congress needs bipartisanship to fully investigate Russian influence MORE (D-Mich.) raised serious questions about whether Pakistan's military and intelligence services had known the whereabouts of Osama bin Laden.

"The Pakistani army and intelligence have a lot of questions to answer," the Senate Armed Services Committee chairman said at a press conference on Capitol Hill Monday, "given the location, the length of time and the apparent fact that this facility was actually built for bin Laden — and its closeness to the central location of the Pakistani army."

Bin Laden was found and killed by a Navy SEAL team in Abbottabad, about 30 miles north of the country's capital of Islamabad. Abbottabad is home to two Pakistani army regiments and many retired members of the Pakistani military.

But Levin said he was reassured by Pakistani President Asif Ali Zardari's statement congratulating the U.S. on its success.

"I do think Pakistan's president's statement was reassuring when he specifically said he thinks it's a great victory, that it's a success, and that he congratulates us on the success of the operation," said Levin. "I am reassured by his statement and not necessarily suspicious that he knew or that the civilian leadership knew."

Since the Global War on Terror began in 2007, the U.S. has provided Pakistan with billions of dollars in aid. Questions have been raised throughout the years about the commitment and loyalty of some components of the Pakistani government and military.

Levin called on that country's civilian leadership to conduct a thorough investigation into the matter.

"But I must tell you that I hope [Zardari] will follow through and ask some very tough questions of his own military and intelligence," said Levin. "They have a lot of explaining to do."

President Obama announced Sunday night that bin Laden had been killed in a U.S. military raid following a firefight in Pakistan. The Pakistani government had not been informed of the operation ahead of time.