Islamic militants Richard Dart and Imran Mahmood were thwarted by Microsoft Word when they held 'silent conversation'

Richard Dart and Imran Mahmood believed they were outwitting surveillance officers when they held a "silent conversation" on a laptop.

As they plotted terror attacks and discussed how to make explosives, they had no idea they were leaving a technological footprint that would eventually build into key evidence against them.

Over many months, police and experts pieced together 2,000 pages of computer codes, painstakingly translating them back into language "character by character" and piecing them together to make the conversation.

In the words of one of the Counter Terrorism detectives involved the practice could be likened to the two terrorists writing on a notepad before ripping out the pages and destroying the paper. However, forensic analysis was able to find the imprint left behind and piece together the shredded conversation.

Mahmood, 22, met Dart, 30, at his Ealing Broadway home on 4 November to discuss plans for terror attacks including one in which they considered targeting grieving families mourning returning soldiers being brought back through Wootton Bassett. They spoke about how to get in touch with the Taliban in Pakistan and al-Qa'ida.

Fearful that they were under surveillance, the pair opened a Microsoft Word document on Dart's laptop and silently typed in their conversation, deleting each page as they went along.

Having failed to obtain terrorist training in Pakistan, Dart was seeking advice from the younger man ahead of a second trip.

Upon their arrest, police seized the laptop and began examining it for evidence with the help of a digital forensics expert. What they found were coded data files within its memory which, once translated, gave them fragments of the conversation.

"These data files would not have been obvious to the users. We pieced them together like paper that has been shredded," said one Detective Sergeant.

By using time data, they were able to put the text together chronologically, enough to realise that the style of the writing, in questions and answers, meant that this was a dialogue between two people.

"The topics of discussion were engaging in terrorist activity, avoiding detection, making explosives and their justification for carrying out attacks in the UK," explained the officer.

Detectives worked out the identities of the two people by the fact that the computer was Dart's and mobile telephone records showed that Mahmood had been in the same location at the time of the conversation. One of the authors of the conversation identified himself as Sulayman, a name Mahmood had used in previous emails.

They then used language idiosyncrasies and particular spelling mistakes to distinguish one from the other. Dart used the term yer repeatedly while Mahmood tended to write in text speak. At one point he said making explosives was "not rocket science lool" (laughing outlandishly out loud). He also repeatedly spelled can as cna, etc as ect and whether as weather, referring to jihad simply as j.

Mr Justice Simon said yesterday: "It is a striking feature of this case that it is your own words Mahmood and Dart that have led directly to your convictions in this case."