Riedel, who was also the erstwhile director for South Asia in the National Security Council during the Clinton Administration and most recently an adviser on foreign policy to the Obama [Images] campaign, said it's difficult to believe the Pakistani government's assertions that its intelligence service has no links to LeT "given the size of its activities in Pakistan."

He said "if there's anything that is a 64 million dollar question today," it is finding out the "extent of its current ties to the Pakistani intelligence service."

Riedel, currently a senior fellow at the Brookings Institution, who keynoted a panel discussion organised by this leading think tank on 'Mumbai terrorist attacks: A challenge for India and the World', acknowledged that "we still need to know much more about the origins of this plot and the masterminds behind it, but we can say for certain today that whoever they were, they were heavily influenced by the ideology and narrative of Al Qaeda [Images]."

He argued that the Mumbai attacks "demonstrates that the ideology and narrative of Al Qaeda and the overall global jihad movement remains potent and continues to inspire deadly terrorism and remains a formidable threat today."

Riedel said, "The massacre in Mumbai will indeed be remembered as a seminal event in the history of international terrorism and particularly in the history of global jihad."

"This was an extraordinarily sophisticated and complex plot that had numerous moving parts and which was executed with -- one has to admit -- a tremendous amount of skill by very well trained terrorists," he added.

Riedel said it was a no-brainer that "there was clearly considerable planning involved in this plot over a protracted period of time," and that the Mumbai attacks "were not a plot by amateurs or by a pick-up group -- this was a plot carried out by professionals, who were trained by professionals who were given a professional plan."

The New York Times reported Wednesday quoting unnamed Pentagon [Images] officials that retired and/or former Pakistani military officials were behind the training of the LeT cadres who carried out the Mumbai attack.

Riedel said the Mumbai carnage "succeeded brilliantly in terrorism's first goal -- to get global attention and to inspire fear throughout the globe, literally millions of people, hundreds of millions of people were fixed to their televisions watching what went on."

He said, "This is the most significant terrorist incident since 9/11," and that in many ways, was akin to 9/11 "in the training and the execution."

Riedel said it was imperative that as the investigation proceeds into the attacks, "We also should consider the possibility that the terrorists deliberately brought with them misleading disinformation to throw investigators off the real scent."

He pointed out that "I have been involved in several investigations of terrorist events in the past, including Pan Am 103 and the lesson I've drawn from them is to be very careful about judging the facts until you have the evidence."

Riedel, who traced the genesis of the LeT, said the group was "an extraordinary radical movement to begin with and over the last decade it has become increasingly radical. It does not seek simply the end of the Indian occupation of Kashmir or to create an Islamic state, in Muslim majority parts of South Asia. Rather, it seeks the creation of a caliphate to dominate all of South Asia, well into Central Asia, something akin in its mind to a recreation of the Mughal Empire."

During the interaction that followed his presentation, Riedel said, "The South Asian community has a tremendous opportunity here to be a bridge between the United States and both India and Pakistan."

He acknowledged that "it's been doing that brilliantly for the last several years. These are the two most successful immigrant groups in American history."

Riedel implored the South Asian American community to "avoid the kind of scandalous attacks on each other which we see in the South Asian press already. We've already got Pakistani television -- one commentator saying that this was a Mossad-Indian plot dreamed up to put the blame on Pakistan -- an exact repetition of the kinds of scandalous, scurrilous attacks that we saw after 9/11."

"Let's be responsible about these things," he said. "Let us let the investigation run its course, and let's try to remember that at the end of the day, there is not a war option here for resolving this question."