An MI5 agent known only as Agent 1603 has appeared in court in New York wearing a long wig and dark glasses to conceal his identity.
The secret agent was giving evidence at the trial of Abid Naseer, a 28-year-old who had planned to attack targets in both Manchester and New York. More British spies are also set to appear over the coming weeks, and have been given dispensation to wear wigs, glasses, and make-up to disguise their appearances.
Agent 1603 was tasked with spying on Naseer in the weeks leading up to his arrest in 2009, and observed him watching videos of the 9/11 attacks on his phone while on a coach trip.
Naseer, who denies all charges, is accused of planning multiple bomb attacks, including ones on the Manchester and New York transport systems, as well as a suicide attack at the Arndale shopping centre.
He was extradited from Britain in 2013. If convicted, he faces a possible life sentence.
The government concedes the two, who are named in the same indictment, never met. In court this week, it was alleged that Naseer used the words "marriage" or "wedding" in emails as code words for explosives. Prosecutors allege Naseer also used the names of women as references to bombs.
In his opening statement, Naseer claimed that he only wrote about women because he was pursuing a bride and was planning an actual wedding.
In a strange twist to the trial, Naseer is representing himself, and on Wednesday cross-examined convicted terrorist Najibulla Zazi who prosecutors say was part of the same al-Qaida conspiracy, all the while referring to himself in the third person.
Naseer questioned how a trained terrorist like Zazi could create a secret email account using a New York City zip code that could tip off authorities about his location. Looking at the account information in evidence, the high school dropout responded that sometimes he's "not very intelligent."