This is a very telling article from a FBI law enforcement bulletin.
Here's a snippet, but the whole article is well worth the read:
"Before intentionally manipulating the media by means of deception, law enforcement officials must consider their actions carefully. For example, many ethics scholars have stated that law enforcement officials should never knowingly present false information to the media.(3) However, suppose a law enforcement administrator conducts an undercover operation designed to expose a ring of narcotics suppliers in a particular area of a city. The administrator may desire to entice the ring to move into another area of the city where undercover officers can purchase narcotics without suspicion. To accomplish this, the administrator drafts a press release announcing the seizure of a large supply of narcotics destined for the area of the city where the undercover officers are operating and gives it to the department press officer, who does not know that it contains false information. After local newspapers print the press release, the undercover officers approach the subjects of the investigation claiming they need a new supplier. This approach succeeds, and the subjects eventually are arrested after passing narcotics to the undercover officers." <snipped>