Police slipped some plastic explosives into a random passenger’s suitcase as part of a test of sniffer dogs. Four days later, the explosives were still missing.
It’s perfectly reasonable to plant an explosive-filled suitcase in an airport in order to test security. It is not okay to plant it in someone’s bag without his knowledge and permission. (The explosive residue could remain on the suitcase long after the test, and might be picked up by one of those trace mass spectrometers that detects the chemical residue associated with bombs.) But if you are going to plant plastic explosives in the suitcase of some innocent passenger, shouldn’t you at least write down which suitcase it was?