provacateurs

"Mr. Darby would not provide details about his undercover activities, but said he had also worked as an informant in cases not involving the convention."
...
"He wore recording devices at times, including a transmitter embedded in his belt during the convention."

January 5, 2009
Activist Unmasks Himself as Federal Informant in G.O.P. Convention Case
By COLIN MOYNIHAN
http://www.nytimes.com/2009/01/05/us/05informant.html