The methods of News of the World investigations editor Mazher Mahmood were again in the spotlight this week as he gave evidence at the Old Bailey.
Mahmood appeared at the trial of three men accused of plotting to make a "dirty bomb" with a mercury-based substance.
In September 2004, the News of the World published a front-page story about an alleged dirty bomb plot after an investigation by Mahmood.
And it was his tip-off to police which led to the arrests of Dominic Martins, Roque Fernandes and Abdurahman Kanyare.
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The reporter's Old Bailey appearance follows calls for his resignation last month by media pundit Roy Greenslade and MP George Galloway, who both condemned his use of subterfuge.
The current trial heard that Mahmood had played the part of a Muslim, called Mohammed, during an undercover operation and claimed that he had nearly a kilogram of red mercury which he was looking to sell.
The current trial is the most high profile Mahmood has played a role in since the 2003 case against five men accused of plotting to kidnap Victoria Beckham collapsed. That case also stemmed from a Mahmood investigation.
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