Channel 4 News Foreign Affairs Correspondent Jonathan Miller exclusively reveals how David Headley - the American linked to the Mumbai attacks - warned of possible strikes just weeks before.
Please wait while this video loads. If it doesn't load after a few seconds you may need to have Adobe Flash installed.
David Coleman Headley was charged in the US for helping to plan the Mumbai terror attack in which 170 people died.
Channel 4 News then revealed how the American, known to friends as "Agent Headley", led a double life in India planning the attack while warning others that an Indian bombing could happen "soon".
This is how Jonathan Miller explained his investigation:
A vast aircraft carrier is docked at the Indian naval base next to Mumbai harbour; dwarfing the cutters and frigates at anchor next to it.
As our ancient wooden tourist boat chugs towards the thronging quayside, the landmarks of the Victorian heart of the city lie dead ahead: the Gateway of India - a towering Moorish-Victorian archway - and the majestic, domed Taj Mahal Palace Hotel.
The Mumbai harbour cruise skipper is watching me: "Navy base," he says, pointing starboard. "No photos, sir, OK? No camera that way."
David Coleman Headley, a white-skinned American-Pakistani, armed with a tourist camcorder and a GPS device, allegedly made an identical trip around Mumbai harbour. Maybe even in this very boat. I wondered if his skipper had warned him too.
Headley, aka Daood Gilani, accused of being the surveillance scout for Pakistani jihadi group Lashkar-e-Toiba - The Army of the Righteous - wouldn't have been much interested in the naval base. That wasn't his target, according to US prosecutors.
The Taj Mahal Palace was though. His alleged mission: to ensure that the attackers who would follow his guidance could kill as many people as possible.
When he took his harbour cruise - some time around April 2008, according to FBI investigators - Headley was hunting for landing sites for what would be remembered in India as 26/11, the devastating maritime terrorist assault on Mumbai in November 2008 in which 170 people died violent deaths and more than 300 were wounded.
The Indian carrier, pride of the fleet, and the cutters and frigates, with all their combined firepower, sat like useless white elephants as a handful of invading jihadis created mayhem nearby.
In this war, good human intelligence was the only meaningful form of defence.
Headley was arrested by the FBI as he was boarding a plane in Chicago in October. He was apparently destined for Pakistan.
In this war, good human intelligence was the only meaningful form of defence.
"I'm convinced Headley was working for the Americans, for the FBI," the man who knew him best in Mumbai, as he staked out his targets, tells me over a double espresso in Barista, a south Mumbai coffee bar where the two had first met. "It was the Americans' deepest wish to infiltrate al-Qaida," says Rahul Bhatt, gun-nut, body-builder, would-be movie star and son of a big Bollywood producer.
"And David did exactly that for them. I had a hunch then and I have a hunch now that he was an American agent of some sort," he says. "I'd nicknamed him Agent Headley."
"You know," he said, nudging his strong, silent companion, another body-builder called Vilas Varak, "he even begged him to get me to stop calling him "Agent Headley" in public. It really pissed him off. Now I know why."
He showed me an email exchange between himself and "Agent Headley".
But in Chicago, the FBI charge sheet, naming Headley as a co-conspirator in the Mumbai massacre, alleges that he was the surveillance scout for Lashkar-e-Toiba - not an American agent.
And that's where this story of the quiet American of Mumbai gets really interesting: who exactly was this former heroin addict and trafficker working for? In a past life, he'd been an informant for the US Drug Enforcement Agency in Pakistan: that's an established fact.
In intelligence circles, it's reported that post-9/11 Headley, the bilingual informant with a foot in both worlds, made the transition from drugs to terror and was recruited by the FBI to infiltrate the jihadist world. That, however, is not an established fact.
But it would explain why the Americans were twice able to warn the Indian intelligence service (the Research and Analysis Wing, RAW) of an imminent terrorist threat to very specific targets in Mumbai - including the Taj Palace and other hotels. The Indian government initially increased security but the measures were dropped before the attacks.
And if Headley had been the source of that very specific intelligence, why, Indians wonder, would he have done that had he really just been a Pakistani jihadi bent on murder and mayhem in Mumbai?
The Indian intelligence services have been denied access to Headley in detention, despite sending a team to Washington DC last month. The heads of the CIA and the FBI have both visited India, however, within the last few weeks.
Meeting Bhatt was the reason I'd travelled to India, although when I left London, I'd had no idea whether we'd convince him to talk. He'd been vilified in the Indian press.
When we met, along with his friend Vilas Varak - aka "Mr Mumbai" (yes, he really had won the local Mr Muscles competition) - Bhatt was wearing a black T-shirt with a machine-gun emblazoned on the front, along with the logo "Uzi does it."
It crossed my mind that in the context of the Mumbai massacre this was a bit tasteless, but I was distracted by the rage and indignation which clearly consumed the two men.
They were angry with the Indian intelligence services, who they said had humiliated them during lengthy interrogations and had been "totally clueless" in their investigations. They were angry with the Indian media for painting them as complicit in the terror attacks.
And they were angry with their erstwhile best friend, David Headley, who'd dropped them in it from a very great height by making the name "Rahul" the byword for Target India: something mentioned six times in the FBI's charge sheets.
"I guess he sold me out on that front," said Rahul. "But you know, he was a great guy. Charming, great sense of humour, caring, sensitive, very well-informed."
David, the 40-something quiet American who loved dogs and cuddling babies, failed to share his double life with his "best buddies" Rahul and Vilas as they munched their way through cheese steaks and fries and apple pie and cream (washed down with Diet Coke) in the Indigo Café, just behind the Taj Palace.
Rahul said he felt betrayed. "I feel hurt, because it's a sort of rape when you have a close friend who..." His sentence dried up. "I have stopped trusting people," he finally said.
The would-be Bollywood star had been cast in the role of a suicide bomber in a film his producer-father wanted to make about the 7/7 bombings in London. David Headley, with his knowledge of the dark arts became a sort of spook guru to Bhatt, 20 years his junior.
After our coffee bar meeting, I met up with Rahul and Vilas again the next day in the Bhatt family apartment, in the rooftop room where they'd often sat talking late into the night with Headley.
"I liked hanging out with him because he... could teach me things about my areas of interest, be it guns, be it intelligence, be it spy-craft. He knew a lot," Rahul said.
There's still a confused air of disbelief in the Bhatt family home over Headley's unmasking - even Rahul's mum admitted to being charmed by him. There's a bit of an "I told you so" thing going on too.
"I liked hanging out with him because he... could teach me things about my areas of interest, be it guns, be it intelligence, be it spy-craft. He knew a lot." Rahul Bhatt
And mixed up with the knowledge that their American "buddy" had dropped them deep in it, I sensed that Rahul Bhatt remains in awe of this shadowman whose tradecraft had allegedly visited such terror on Mumbai.
Rahul Bhatt and Vilas Varak are not off the hook.
They remain tainted by association with David Headley. But they want to forgive his apparent betrayal. "This is an email he sent us on 11 December 2008," Rahul said. That's two weeks after the massacre ended. "He says: "Hey guys, so sorry to see what has happened in Mumbai. We should go over there and kick their ass"."
"Would you go and see him in jail?" I asked.
"Oh, definitely," the immediate, joint response.