WASHINGTON: US Defense Secretary Leon Panetta still believes someone in authority in Pakistan knew where Osama bin Laden was hiding before US forces went in to find him, he said in a TV interview to air Sunday.

Intelligence reports found Pakistani military helicopters had passed over the compound in Abbottabad, Pakistan where US Navy SEALs discovered and killed bin Laden last year, according to excerpts of an interview Panetta gave to CBS News.

"I personally have always felt that somebody must have had some sense of what was happening at this compound. Don't forget, this compound had 18-foot walls... It was the largest compound in the area.

"So you would have thought that somebody would have asked the question, 'What the hell's going on there?'" Panetta told CBS.

The Pentagon chief said that concern played a significant factor in Washington not warning Pakistan officials of the impending raid: "it concerned us that, if we, in fact, brought (Pakistan) into it, that-- they might...give bin Laden a heads up," he said.

Panetta acknowledged he did not have "hard evidence" Pakistan knew of the Al Qaeda leader's whereabouts.

US Navy SEALs killed Bin Laden on May 2 in a raid on a compound in the Pakistani garrison town of Abbottabad, north of the capital Islamabad, and later buried the 9/11 mastermind at sea.