In Cesar, Magdalena, and La Guajira, three departments in northern Colombia, police have called on civilians to volunteer to be informers, passing on information about rebel movements or attacks.
Codenamed "Stakeknife" the man in charge of hunting down informers in the ranks was one of the biggest informers of all for nearly two decades.
This article here looks at some of the techniques used by police to recruit informers in political groups.
The investigation was launched after four campaigners alleged that they felt intimidated by police officers who were trying to turn them into informers.
Their ranks have been penetrated by informers and agent provocateurs for more than a century.
Codenamed "Stake Knife", this son of an Italian immigrant was in charge of the so-called "head hunters", the unit that searched for, tracked down, brutally interrogated and then killed suspected informers.
It is likely that police forces across the country have turned political activists into informers.
It continued to evolve as signals intelligence – Sigint, as the agencies call it – became as important as human intelligence (Humint) – recruiting "moles" and informers.
Cambridgeshire police are carrying out the internal investigation into what they have described as serious allegations surrounding its attempted recruitment of informers.
Police are believed to be running hundreds of informers in political groups across the country, but little is known about them.
However approaching campaigners to become informers can - for the police - be hazardous, as this article examines.
