A senior former Pakistani intelligence official put it more bluntly. "These (ethnic) Pashtuns have their own traditions. They'll die but they'll not hand over bin Laden," said the official, who declined to be named because of the secretive subject matter.

For U.S. troops, the Afghan mission is increasingly dangerous. At least 272 U.S. service members have died in and around Afghanistan since October 2001, including three recently from Williams' unit. Some 44 U.S. servicemembers died in Afghanistan in 2004, 92 in 2005 and 61 so far in 2006.

Western, Afghan and Pakistani officials agree that the nearest they got to bin Laden was in the Tora Bora mountains, south of Kunar, in November 2001 when he was fleeing the U.S.-backed war that toppled the Taliban regime.

The Pakistani intelligence official said Pakistan at first thought bin Laden was dead, perhaps killed by a bomb at Tora Bora, until a letter he penned to his family was recovered from Khalid Sheikh Mohammed when he was arrested in March 2003.

After that, repeated attempts have been made to get bin Laden and al-Zawahri.

• In late 2003, Pakistani forces raided Lattaka, a village in North Waziristan, to get bin Laden but he wasn't there, said the intelligence official.

• In 2004, amid a flurry of military action on both sides of the border, U.S. Lt. Gen. David Barno said he expected to bring bin Laden to justice that year — although officials now say they had no hard intelligence to go on.

"It was all guesswork. No one ever gave us precise information that bin Laden or al-Zawahri is in such-and-such area, even a general area," said Pakistan's Aurakzai.

• Pakistan stepped up its military action in 2004 with a series of bloody operations in South Waziristan province. They busted al-Qaida bases complete with computer and communications equipment. However, most foreign militants at these sanctuaries were not Arabs close to bin Laden but Central Asians, Pakistani officials said.

• Sometime that year, Pakistan learned that either bin Laden or al-Zawahri was elsewhere in South Waziristan. "An operation was carried out where we were close to getting him but the trail got cold," said Maj. Gen. Shaukat Sultan, spokesman for President Pervez Musharraf. He declined to be more specific.

• In the most recent case, in January, the CIA fired a missile from a Predator drone into the remote Pakistani village of Damadola, 155 miles northeast of Waziristan. The target was al-Zawahri, who was expected to attend a dinner there. Pakistani intelligence and local residents say the Egyptian doctor-turned-terrorist did not show, but they later learned he was at a supporter's home in Salarzi, about 7.5 miles to the east.