Defense Secretary Donald Rumsfeld said Wednesday he did not have enough evidence to prove or disprove a report the United States had blown a chance to capture or kill Usama bin Laden last year in the Tora Bora cave complex.

It is "entirely possible" bin Laden was in the Tora Bora region when American forces began their bombing campaign there in December, Rumsfeld said, responding to a barrage of questions related to bin Laden. But "in terms of any solid evidence, there wasn't any. There isn't now," Rumsfeld told reporters.

The questions came in response to a Washington Post story that bin Laden had escaped the battle of Tora Bora after the U.S. decided it would not commit American ground troops to the operation.

"We [messed] up by not getting into Tora Bora sooner and letting the Afghans do all the work," a government official was quoted as saying in the Post.

The official quoted by the newspaper and a number of military officials have said the decision not to commit U.S. ground troops to Tora Bora was a grave mistake. Military commanders have since changed that policy, as evidenced by the more active U.S. military action in Operation Anaconda.

The Post said the decision not to commit the U.S. troops in Tora Bora came from Gen. Tommy R. Franks, the war's operational commander. Several officials in the Post story blamed Franks for not recognizing the mistake quickly enough, and changing his policy only after bin Laden and a number of his Al Qaeda fighters escaped.

The initial U.S. policy to rely on Afghan "allies" to lead the fighting against Taliban and Al Qaeda forces was criticized in some circles almost from the start of the fighting in October. The critics argued that U.S. allies like the Northern Alliance and anti-Taliban Pashtun militias consistently allowed enemy forces, including Al Qaeda troops, to escape across the Afghan border into Pakistan.

Several press reports at the time noted the Afghan forces in Tora Bora had left open a number of escape routes for Taliban and Al Qaeda troops during and after the battle. Allowing the enemy to lay down their arms and leave the battleground is an established tradition in Afghanistan.

Rumsfeld declined to comment on the specifics of the Tora Bora command decision to leave U.S. ground troops out of the fighting. But he did defend his commanders, portraying criticism of their actions as Monday morning quarterbacking.

"I don’t think there’s ever been a battle or a war where there weren't be people sitting around in Washington, D.C., or outside the zone opining on what should have been done," he said.

Franks reportedly told subordinates it was vital at the Tora Bora battle — among the first to include allies from Afghanistan's Pashtun majority — to take a supporting role and "not just push them aside and take over because we were America," according to the Post.

It's not clear how many Al Qaeda or Taliban forces may have escaped Tora Bora and crossed into Pakistan. The U.S. has since asked the Pakistani government to step up efforts to crack down on the border, and has quietly engaged in military operations within Pakistani territory.

Just two of the top 12 Al Qaeda leaders identified by the U.S. government are currently accounted for. Muhammad Atef is presumed dead following a missile attack, and Abu Zubaydah was taken into custody late last month.

A number of others believe bin Laden has been dead for weeks or even months. They note he has not been heard from, at least in any way where his survival could be proven.

Rumsfeld said Wednesday U.S. commanders received numerous reports about bin Laden's whereabouts in recent months, but could not confirm any of them.

"We literally see speculation about his location on a regular basis," Rumsfeld said.