But how do we know there really was a plot?
That's essentially the question behind a documentary premiered at the Sundance Film Festival this week which gained unprecedented access to a real-time FBI counter-terrorism "sting" -- and found some disturbing answers.
"Evidence suggests that in these cases these informants are not going into communities simply to monitor and collect evidence on terrorism," said David Sutcliffe, co-director of "(T)ERROR."
"They themselves are the ones posing the inducements and suggestions for criminal activity," he told AFP in an interview with fellow filmmaker Lyric Cabral in Park City, Utah.
The documentary tells the real story of "Shariff," a 63-year-old informant for the Federal Bureau of Investigation (FBI) who is tasked with monitoring a Muslim convert, Khalifah al-Akili, in Pittsburgh.
The FBI wants him to assess Akili's interest in attending a terrorist training camp abroad.
We see "Shariff" -- real name Saeed Torres, a former black revolutionary turned school canteen cook, and practising Muslim -- as he befriends Akili through a local mosque.
The unprecedented part? The FBI doesn't know its informant has agreed to be filmed for the documentary.
The background: "Shariff" had worked for the FBI for over two decades and was earning hundreds of thousands of dollars in his prime. But he is down on his luck after his cover was blown in 2005, when he had to relocate overnight from New York to South Carolina, and is scraping by.
"He was just essentially a man out in the cold," said Sutcliffe. "They'd bring him in for random cases. But he was looking for a different path, and he felt that this (the film) was an opportunity."
- Sting collapses -
Training for FBI informants is apparently pretty rudimentary: the agency set up a Facebook account for "Shariff" to keep in touch with his target, but didn't show him how to use it.
And his FBI handlers' incompetence is shown to be responsible for blowing his cover for a second time, this time spectacularly, although Akili still ends up being jailed for eight years.
The number of FBI informants "exploded" after the September 11, 2001 attacks, from 1,500 before to 15,000 by 2008, said Sutcliffe. "The number may have even increased since then," he said.
Coincidentally, a US man was arrested only two weeks ago for allegedly plotting an attack on Congress inspired by Islamic State jihadists, according to the Justice Department and the FBI.
US House Speaker John Boehner said that the plot was foiled thanks to the government's controversial surveillance programs, allowed under the Foreign Intelligence Surveillance Act (FISA).
But the filmmakers are not convinced.
"There are certain details... that lead us to believe that the informant had a similar role in that case to Akili's case in the film," said Sutcliffe.
"The FBI's argument is that it really takes a criminal to catch a criminal," said Cabral, adding that the recordings of evidence are rarely released because most cases do not go to trial.
"Often the public doesn’t have the benefit of hearing what it is that the informant says to get (the target to implicate themselves). Just how does one encourage someone to speak about terrorism?
"The American government will never hear those tapes unless someone goes to trial."
Cabral says she hopes their film -- in the US Documentary Competition at Sundance, which ends this weekend -- will lead to a debate.
"We hope to stimulate a public dialogue about the FBI's use of informants and to enlighten the American public about the strategies and methods which the FBI uses to secure these terrorism convictions," she said.
