| plainclothes officer(expression, agent, informer, reporter) |
| police officer(expression, agent, informer, reporter) |
| prosecutor(agent, informer, reporter, gumshoe) |
| reporter(agent, informer, gumshoe, investigator) |
| roper(agent, informer, reporter, gumshoe) |
| sergeant(agent, informer, reporter, gumshoe) |
| shoofly(agent, informer, reporter, gumshoe) |
| slewfoot(agent, informer, reporter, gumshoe) |
| spook(noun, plant, agent, operative) |
| tap(verb, bug, monitor, poke) |
| undercover agent(noun, expression, plant, agent) |
| wiretap(bug, monitor, poke, tap) |
| bend an ear(expression, idiom, bug, monitor) |
| ears into(expression, bug, monitor, eavesdrop) |
| infiltrator(noun, plant, mole, detective) |
| monitor(bug, eavesdrop, overhear) |
| nose round |
| wire(bug, monitor, eavesdrop, overhear) |
| work undercover(verb, expression, discover, pry) |