Is there a term for a police officer or someone else working for a country's security forces who masquerades as an inmate and is put into a cell with a suspect in order to extract information?

I'm not sure that informant works here..

  • 1
    Also a plant. . .
    – Xanne
    Nov 25, 2019 at 16:02
  • @MichaelHarvey I think stool pigeon is something different than questioner is describing. A stool pigeon would be used for a real inmate who grasses or informs, as opposed to a planted undercover officer.
    – k1eran
    Nov 25, 2019 at 22:25

2 Answers 2


I think most people would use the informal and colloquial word mole:

4 : a spy (such as a double agent) who establishes a cover long before beginning espionage
broadly : one within an organization who passes on information

Wikipedia says more about its applicability to police officers specifically:

In police work, a mole is an undercover law-enforcement agent who joins an organization in order to collect incriminating evidence about its operations and so bring its members to justice.

  • Seems to me that would mean that a mole is planted in order to catch police officers... but I'm looking for the guy used against ordinary criminal suspects, terror operatives, etc.
    – Ilanysong
    Nov 26, 2019 at 7:28
  • @Ilanysong In police work, a mole is a police officer who is planted to catch somebody in some organization. It could be somebody from internal affairs (a police officer trying to catch other police officers), but that would be unusual. In almost every case, a mole is planted to catch so-called regular criminals. Nov 26, 2019 at 14:32
  • I see. I'm quite ignorant on police work, so I'll take your word for it! Thanks!
    – Ilanysong
    Nov 28, 2019 at 8:06

I think I would probably use infiltrator as a general term, though more specifically, in this situation an undercover police officer.

As the below quotation from the OED will illustrate, the verb infiltrate is used figuratively, in a political sense, normally to describe a process of political subversion. However armies and law enforcement authorities can and have infiltrated the hierarchies of insurgent and subversive movements in order to gain information.

It has been a method, used by Britain in colonial situations against such as the Mau Mau in Kenya, and the Communists in Malaya. It was also a process which played a big part in the destabilisation of the IRA in Northern Ireland.

Police forces infiltrate criminal gangs, and hence the placing of an undercover officer in a cell would seem to me to amount to much the same thing - to gain information on a wider criminal organisation, or group of accomplices.

Infiltrate-verb 4. Military. transitive and intransitive. To penetrate (enemy lines) by the gradual or surreptitious movement of small numbers of troops; to move (one's own troops) surreptitiously into the enemy's lines. Also figurative, esp. for the purpose of political subversion.

  • Thanks for your suggestion - infiltrate would definitely be the right verb to use in this context. Undercover police officer works fine, too, I prefer mole because it's "short and sweet :).
    – Ilanysong
    Nov 28, 2019 at 8:08

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