On any given day, more than 15,000 informants are collecting information for the US Federal Bureau of Investigation (FBI). Many work in Muslim communities, often posing as members of groups like al-Qaeda. They create plots and offer community members opportunities to get involved. So, who are these informants and what are their motivations? A new documentary by Al Jazeera's Investigative Unit goes inside the secret world of FBI informants and counter-terrorism operations. We discuss Informants at 1930GMT.