“In jurisdictions in which conspiracy is a serious crime in itself, it can be sufficient for the agent provocateur to entrap the target into discussing and planning an illegal act. It is not necessary for the illegal act to be carried out or even prepared.
“Prevention of infiltration by agents provocateurs is part of the duty of demonstration marshals, also called stewards, deployed by organizers of large or controversial assemblies. ...
“While the practice is worldwide anciently, modern undercover operations were scaled up in France by Eugène François Vidocq in the early 19th century, and already included use of unlawful tactics against opponents. Later in the same century the police targets included union activists who came to fear plain-clothed policemen (agent de police in French). Hence, the French agent provocateur spread, just as is, to English and German. In accordance with French grammar, the plural form of the term is agents provocateurs.”**
--------------------------------------------/
**https://en.wikipedia.org/wiki/Agent_provocateur (Bold emphasis added.)