The New York Times reports on the increasing use of undercover agents by the federal government:

Undercover work, inherently invasive and sometimes dangerous, was once largely the domain of the F.B.I. and a few other law enforcement agencies at the federal level. But outside public view, changes in policies and tactics over the last decade have resulted in undercover teams run by agencies in virtually every corner of the federal government, according to officials, former agents and documents.

Across the federal government, undercover work has become common enough that undercover agents sometimes find themselves investigating a supposed criminal who turns out to be someone from a different agency, law enforcement officials said. In a few situations, agents have even drawn their weapons on each other before realizing that both worked for the federal government.