U.S. and European intelligence officials increasingly believe active or retired Pakistani military or intelligence officials provided some measure of aid to al Qaeda leader Osama bin Laden, allowing him to stay hidden in a large compound just a mile from an elite military academy.

The suspicions cast light on where the U.S. is expected to focus as it investigates who might have helped bin Laden hide in plain sight in Abbottabad, a town about 40 miles from the capital Islamabad.

Two...