The Seige: Three Days of Terror inside the Taj

"Headley only served himself," said Adrian Levy, who has written "The Siege: Three Days of Terror Inside the Taj" along with co-author Cathy Scott-Clark, at a session at the Jaipur Literary Festival 2014 Saturday.

Given his background - a Pakistani father and an American mother - Levy said that explains why Headley betrayed everyone he came in contact with, his friends when he became a drug dealer, the drug syndicates when he became an informer for the US Drug Enforcement Administration and then later US intelligence and his jihadi masters with wider consequences.

Listing why Headley was so sought after by US intelligence, Levy said this was because Headley was convincing, difficult to control and all these attributes made him "attractive for intelligence agencies".

"Also he was the only American passport holder that could lead the US security agencies to Osama bin Laden," said Levy.

On how much Pakistan's Inter-Services Intelligence (ISI) knew about 26/11, he said he asked himself the same question.

"Lashkar-e-Taiba, like other jihadi outfits, has a lot of ex-servicemen and ex-spies who may not be ex," he said, adding this has been a hallmark of such outfits right from the time when Zia-ul-Haq consolidated power.

Levy said that while researching the book, he used the services of an efficient firm of civilian career investigators, but even they had no idea about the LeT.

"They knew everything about the Sipah-e-Sahaba Pakistan, the location of all bomb factories in Miranshah (capital of North Waziristan), but nothing about the Lashkar... nobody knows. It's a manifestation of the state and digging about it is discouraged," he said.