While the civilian government of Pakistan denies that the ISI was involved in the attack on Mumbai, their denial has to be recognized as necessary because if they failed to deny the ISI involvement then they would be admitting that the Pakistan government is so weak that it cannot prevent rogue elements of the ISI from attacking Pakistan's neighboring countries. Admission of that weakness could easily attract internal opponents to try to replace them. The same dynamic applies to the public complaints the government makes about the American drone strikes against the Taliban in North Wiziristan even though elements of the government are said to be providing targeting information to the Americans in order to guide the drone attacks.Pakistan's powerful intelligence service has been accused for years of playing a "double game:" acting as a front-line U.S. ally in the fight against terror while supporting selected terrorist groups which serve Pakistani interests.
Now, for the first time, there is a detailed inside account of how that game is played. The U.S. investigation of the 2008 Mumbai attacks  has built a strong case that officers in Pakistan's Inter-Services Intelligence Directorate (ISI) collaborated with the Lashkar-e-Taiba terrorist group in the plot that killed 166 people, six of them Americans. U.S. and Indian investigators say their understanding of the ISI-Lashkar alliance is drawn from the confessions of David Coleman Headley, an American convicted of participating in the Mumbai plot, as well as documents, phone records and electronic eavesdropping.
Officials from both countries say they are persuaded that ISI officers recruited and trained Headley in spying techniques and gave him money and instructions to scout targets in Mumbai and elsewhere. Headley has told investigators that a Pakistani Navy frogman helped plan the maritime attack on Mumbai, according to a 119-page report recounting his interrogation this year by Indian authorities. The report, which was obtained by ProPublica, quotes Headley as saying his Pakistani intelligence handler took part in a discussion about a subsequent Lashkar plot to attack a Danish newspaper -- information that Pakistan did not share with Danish authorities.
In essence, U.S. and Indian officials say, Headley was more than a terrorist: He served as a Pakistani spy.
During the period that ISI officers allegedly helped Lashkar plan to kill Americans and Jews in Mumbai, the intelligence service was working closely with the CIA and U.S. military in counter-terrorism efforts and Pakistani President Asif Ali Zardari was pledging his support for the U.S. campaign against militants in Pakistan and Afghanistan.
Pakistani officials deny any link to Lashkar and point out that hundreds of ISI officers have died in clashes with militants. They accuse India of politically motivated distortion in the report on Headley's interrogation.
"It is a stereotype, a Pakistan-specific version of an Indian interrogation," said a Pakistani official who requested anonymity because of the sensitive topic. "The Indian version is totally distorted and fabricated as there was no involvement of the ISI whatsoever. Nor did any serving official interact with Headley or any of the perpetrators."
But U.S. investigators see much of Headley's account as credible, U.S. officials said. The investigators believe his main handler, a man identified only as Major Iqbal, was a serving member of ISI and one of several Pakistani intelligence officers who had contact with Headley, according to U.S. officials.
The Obama administration has expressed frustration with Pakistan's failure to bring to justice the suspected masterminds of Mumbai and to rein in Lashkar, the ISI's longtime proxy army against India. Recent intelligence shows Lashkar remains intent on striking the West, according to a U.S. official who requested anonymity.
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