If they had seized the video and destroyed it, one or more of the cops involved might actually have faced some kind of internal discipline. This way, they get to place the blame entirely on the informant. They can make a statement like “Informants are an important part of the law enforcement process. On rare occasions, an informant may perform unlawful activities under the mistaken impression that it would help law enforcement. Let me be clear: we do not want that kind of help. Our officers had no knowledge of what the informant intended to do nor do they know where he obtained the substance placed on the counter. Now we will be doing everything possible to track down this man. He is (insert description of informant). If you or any other member of the public has information about him, call Crimestoppers at 1-800-222-TIPS”