By Jeremy Britton
BBC News, the Old Bailey
Five men have been convicted of conspiring to cause explosions after a trial at the Old Bailey. A key prosecution witness was Mohammed Babar, a former terrorist who became a supergrass.
MOHAMMED JUNAID BABAR
Born near Peshawar, Pakistan in 1975
Moved to the US at the age of two and lived in New York City
Left school at 19 and studied pharmacy at St John's University in Queens
Dropped out after a year and worked as a valet and a security guard
Went to Pakistan, via London, nine days after 9/11
In November 2001 he told a British TV reporter he would kill US troops who came to Afghanistan
Between April and October 2002 he was employed as a regional manager by Pakistan's Software Export Board
Returned to the US in April 2004 and was arrested by the FBI shortly after
To the press he was a supergrass. To his co-conspirators he was a traitor to the cause. But to US and British police and intelligence services, the witness Mohammed Junaid Babar was something even more important - he represented the future of the war on terror.
If al-Qaeda operatives can be made to plead guilty in return for a lighter sentence and testify against their former "brothers" in court, then not only are the chances of convicting suspects dramatically raised, but the morale of the organisation suffers a big hit.
The Mafia suffered a similar blow when supergrasses like Tommaso Buscetta and Jimmy Fratianno began co-operating with the authorities in the 1970s and 1980s.
They have been followed by hundreds more, in both Italy and the United States.
Babar's appearance in the Old Bailey was the biggest test of an al-Qaeda informant so far in Britain - and it proved absolutely crucial to the prosecution's ability to bring down a network of conspirators.
In legal jargon they are known as "CWs", co-operating witnesses. In Babar's case his reasons for co-operating were obvious. If he did not help the FBI he risked facing a lengthy prison sentence for terrorism.
Tommaso Buscetta: Mafia supergrass - could the same work for al-Qaeda?
Babar also feared being returned to Pakistan where he said he could face the death penalty for helping to organise two assassination attempts against President Pervez Musharraf.
Instead, he told the court, he now hoped to walk free in the US in as little as three years' time.
Like all deals there were strings attached. Under his plea bargain in a New York court Babar was required to give evidence to any US agency at any time. But if he lied in court the deal was off.
There is little doubt he was well trained for the trial. From the outset he gave short, precise answers to every question and spoke softly, looking directly at the jury. He avoided eye contact with the defendants.
Babar had memorised his statement to the British police, given to counter-terrorism officers while he was in custody in the US, and knew every date and location in the long story of the conspiracy.
Babar also had a good story to tell - how he, a car cleaner in New York, had travelled to Pakistan soon after the 9/11 attacks and joined the "jihad" - the shorthand used by militant Islamist fighters to describe their theological justification for taking up arms.
He told how his house in Lahore became a base for militant Islamists and how he organised a training camp for many of the defendants.
Key meeting: Waheed Mahmood's house in Pakistan
Within three years he was paying visits to a senior al-Qaeda figure called Abdul Hadi - and even acting as a peace-maker between rival militants in the UK.
His evidence made headlines. One by one he named his fellow conspirators and described the plots they discussed - blowing up New York's Times Square, spiking the drinks at football matches with poison and a suicide bomb on the London underground.
But under rigorous cross-examination cracks began to appear in his carefully prepared account.
Babar's early evidence had answered two crucial questions: why had the defendants decided to attack the UK when they appeared to want to fight in Afghanistan? And who would provide the detonators that would be needed to set off any fertiliser bombs?
Babar described how some of the defendants had met the Pakistan home of Waheed Mahmood, one of those found guilty, in 2003 for a crucial discussion. The men wanted to go and fight against US forces in Afghanistan.
But Mahmood told them there was no chance of getting across the border. Instead the UK should become their target for its role in the military campaign.
Under cross-examination Babar became increasingly uncertain about the meeting. Maybe there were two events, he told the jury. Maybe some of the defendants were not there. The defence suggested there was no such meeting at all.
Babar also described how the defendant Salahuddin Amin, then living in Pakistan, had given him a bag of detonators, which were intended to be taken to the UK via the Middle East. But again under cross-examination he seemed unsure.
At the end of his evidence the jury themselves sent a note asking him to describe again just how the detonators were handed over. Babar seemed confused as to how many bags the detonators were wrapped in.
The defence remained deeply suspicious about why Babar, a committed jihadi was picked up off the streets of New York by the FBI and implicated his fellow colleagues.
Several defence lawyers suggested Babar was in fact a US agent who could have been recruited in 2004 when he visited the US embassy in Pakistan to ask for a visa for his family to return to America.
Why would the US grant a visa to a man who had told a British television reporter in 2001 that he wanted to kill American soldiers in Afghanistan, they asked? That was treason and he should have been arrested.
The guilty convictions undoubtedly show the advantages of evidence from witnesses like Babar. Yet his full story and real motivation remain unknown.
When Babar is released he will go into a witness protection programme. The question is how many more will follow his example.