Of all the material which I acquired in the course of making my documentary, Terror in Mumbai, it is the phone intercepts - recordings by Indian intelligence of mobile phone traffic between the young gunmen and their handlers back in Pakistan - which I found the most chilling.
The close-up rustling, the tense silences, the gunshots, the amazement at the luxury of the five-star hotels which continued to amaze me every time I played back the recording during the edit. And above all the horrifying, dead-pan practicality of the preparations for taking the lives of innocents.
The first clue that the terrorists' phone calls had been tapped during the Mumbai attacks last November came when the Indian government released a dossier pointing an accusatory finger at Pakistan.
This was classified material, perhaps some of the most important wiretaps ever recorded by the Indian secret services. Yet one morning four months later I returned to my hotel room in Mumbai looking over my shoulder and clutching a set of recordings. Soon the long-dead voices were playing through my headphones.
I don't speak Urdu or Punjabi but found myself listening compulsively to file after file, trying to guess what was going on, mesmerized by the contrast between the coy, remarkably gentle voices of the young gunmen and the jaded, business-as-usual tone of their middle-aged handlers.
As I read the transcripts of the phone calls, it dawned on me that the raid on Mumbai was a brilliantly devised piece of horrific terrorist show business.
The 10 gunmen had sneaked ashore in Mumbai around 9pm on 26 November, having sailed from Pakistan in a hijacked Indian trawler.
Less than an hour later, during a killing spree across the city which included the main railway station, four gunmen entered the luxury Taj Hotel. Young Pakistanis from villages in the Punjab, who had never set foot in a modern hotel before, let alone the vast suites on the upper floors of the Taj, they could not contain their amazement. The first few hours of intercepts at the Taj show them struggling to keep their minds on the task of burning down the hotel.
'There are so many lights... and so many buttons. And lots of computers with 22 and 30-inch screens...' says one.
The other chilling piece of evidence we obtained during the making of this film, was told by one of the gunmen, Kasab, who was taken alive by Indian police and his questioning recorded.
'What's your gang called? Your team?' asks one policeman.
Kasab seems not to understand.
'Your organization, your gang, you team?', some of the other officers round the hospital bed chime in.
'Oh... It's Lashkar e Toiba.'
When asked about the massacre at the railway station, Kasab is equally direct:
'They told us we had to do this job,' explains Kasab.
'What job?' asks the cop.
'The VT station job' – CST station is still known to many by its old colonial name VT, Victoria Terminus.
'What do you mean by 'the job'?'
'I was supposed to kill people there?'
Next the policeman tries to figure out what the terrorists' exit strategy was: 'After completing your job today, where were you going to go?'
'We were all going to die,' says Kasab matter-of-factly.
'How's that?' asks the cop.
'He told us we'd be going to heaven,' replies Kasab.