In a report in the island's Sunday Times newspaper, defence analyst Iqbal Athas said up to 27 elite rebel fighters were able to stroll into the Anuradhapura base unchallenged before unleashing their assault.
Authorities had previously said the rebels had sneaked into the base by cutting through the barbed wire perimeter.
"Up to 27 Black Tiger suicide cadres were able to go unchecked right up to the aircraft hangar," the report said, adding that the guerrilla strike force had camped at a nearby abandoned house before entering the military complex.
"There is no doubt that the guerrillas have been receiving up-to-date intelligence on the lay out and goings on at the air base," the report said.
"There was inside information," it said, adding security at the base may have been compromised due to the use of casual labourers hired to carry out runway expansion work.
Athas said the government may have also played down the damage inflicted during last Monday's attack.
Officials have