An FBI informant who attempted to infiltrate an Islamic community centre in the quiet Californian town of Irvine scared Muslim worshippers so much with his talk of violent jihad that they took out order against him, the Washington Postreported.
The FBI claims its use of such informants has prevented more attacks since the attacks of September 11, 2001.
Yet its officials have said that they do not target Muslims - an argument that has long been taken with a dose of scepticism by some commentators.
The latest case follows revelations that a man who tried to bomb a Christmas ceremony in Portland, Oregon, did so not only whilst under FBI surveillance, but had been provided with fake explosives by its undercover agents.
Making matters worse for the agency, Craig Monteilh, the convicted fraudster whom the FBI sent into the mosque to spy on its members, has gone public and is suing the investigative agency.