Doubts about the veracity of the intelligence, fears over killing civilians, and worries over alienating allies in the region were cited by policymakers as reasons for not acting, according to the National Commission on Terrorist Attacks Upon the United States.
"Each time the munitions and the people were spun up, they were called off because the word came back: We're not sure -- we're not quite sure," former US defense secretary William Cohen told the commission at a hearing here.
"In one instance, there was an identification that somehow we had bin Laden in our sights. Turned out it was a sheikh from UAE," he said.
"There was another consideration of shooting down an aircraft that might be carrying bin Laden, should he try to escape. That also proved to be reversed by the intelligence community saying we don't think we have him," he said.
The commission, however, reported that a CIA field officer believes that the episode involving the UAE sheikh was a lost opportunity to kill bin Laden before the September 11, 2001 attacks on the United States.
In a report on its initial findings, the commission disclosed three occasions in which bin Laden was in US sights, and a fourth that is still under investigation.
They occurred in the months after the August 11, 1998 bombings of the US embassies in Nairobi and Dar es Salam, the report said.
The Pentagon had launched cruise missiles at a training camp in Afghanistan where bin Laden was believed to be meeting with terrorist leaders on August 20, but failed to kill him.
In December 1998, the United States readied a new set of strikes after receiving intelligence that bin Laden was staying at a particular location in Kandahar, the report said.
But then-president Bill Clinton's top advisers recommended against the strike, it said.
CIA director George Tenet "told staff that the military, supported by everyone else in the room, had not wanted to launch a strike because no one had seen Osama bin Laden in a couple of hours," according to the report.
Tenet told the commission "there were concerns about the veracity of the source and about the risk of collateral damage to a nearby mosque." Richard Clarke, the former White House counter-terrorism chief, told the commission that the intelligence was regarded 50 percent reliable, and there was a risk that 300 civilians could be killed.
The next opportunity came in February 1999 after US intelligence reported that bin Laden frequently visited a hunting camp in Afghanistan's Helmand province that was frequented by visitors from the United Arab Emirates.
"At the beginning of February, bin Laden was reportedly located there and apparently remained for more than a week," said Philip Zelikow, the commission's executive director.
"This was not in an urban area so the risk of collateral damage was minimal. Intelligence provided a detailed description of the camps. National technical intelligence confirmed the description of the larger camp and showed the nearby presence of an official aircraft of the UAE," he said.
Preparations were made for a strike, but it was never launched.
"According to CIA officials, policy-makers were concerned about the danger that a strike might kill an emirate prince or other senior officials who might be with bin Laden or close by," Zelikow said.
"The field official believes today that this was a lost opportunity to kill bin Laden before 9/11," he said.
The next chance to kill bin Laden came in May 1999 when sources reported in detail on bin Laden's whereabouts in Kandahar over a five-day period.
But CIA officials were told the strikes were not ordered because of concern over the precision of the source's reporting and the risk of collateral damage.
"Having a chance to get OBL (Osama bin Laden) three times in 36 hours and forgoing the chance each time has made me a bit angry," the chief of the unit tracking bin Laden wrote to a frustrated colleague.
"The DCI (director of central intelligence) finds himself alone at the table with the other principals basically saying, 'We'll go along with your decision, Mr. Director,' and implicitly saying, 'The agency will hang alone if the attack doesn't get bin Laden,'" the reported quoted him as writing - Sapa-AFP