The Guardian is reporting on a ten year old deal between the US and Pakistan to allow American forces to move into Pakistani territory without permission if they knew were OBL was hiding:

The US and Pakistan struck a secret deal almost a decade ago permitting a US operation against Osama bin Laden on Pakistani soil similar to last week's raid that killed the al-Qaida leader, the Guardian has learned.

The deal was struck between the military leader General Pervez Musharraf and President George Bush after Bin Laden escaped US forces in the mountains of Tora Bora in late 2001, according to serving and retired Pakistani and US officials.

Under its terms, Pakistan would allow US forces to conduct a unilateral raid inside Pakistan in search of Bin Laden, his deputy, Ayman al-Zawahiri, and the al-Qaida No3. Afterwards, both sides agreed, Pakistan would vociferously protest the incursion.

"There was an agreement between Bush and Musharraf that if we knew where Osama was, we were going to come and get him," said a former senior US official with knowledge of counterterrorism operations. "The Pakistanis would put up a hue and cry, but they wouldn't stop us."

The deal puts a new complexion on the political storm triggered by Bin Laden's death in Abbottabad, 35 miles north of Islamabad, where a team of US navy Seals assaulted his safe house in the early hours of 2 May.

If either President Obama or President Zardari would reveal the details of such an agreement, it would destabilize the Pakistani government. In fact, most counterterror assistance Pakistan gives the US is on the sly because of the anti-US elements in government and the military. Zardari's enemies could use any cooperation with the US as political leverage and weaken an already weak government.

This doesn't mean that OBL's whereabouts weren't known to the highest levels of the Pakistani government.  But it does shed some light on their reaction to the raid and why Obama felt he could go in despite what would appear to be a violation of Pakistan's sovereignty.