Alvarez, Las checas del Madrid Republicano: un ejemplo de investigación interdisciplinar, [in:] Aportes' 79 (2012), p. 79</ref> During first months of the war they by far eclipsed state formations in terms of shaping the public order ambience in Madrid, yet due to their makeshift organization, ephemeral nature and improvised modus operandi this vast force evades systematic structural description. These groups are best known because of detention and interrogation posts operated, commonly known as checas; their number is currently calculated at around 350, some 4 per every square kilometer and one per every 3,000 people; the majority disappeared by early 1937. Though there are rare accounts of conflict between militias and official public order units, in general the latter avoided challenging the former. Both developed sort of operational symbiosis, e.g. militias used official police records to identify and locate suspects, at times handed over detainees to DSG or – far more frequently – took them over from prisons, arrests or police stations. It is suspected that on exception basis frontline military units might have also participated in action against presumed anti-Republican conspiracy. In August 1936 the DSG in agreement with major parties decided to set up a new body, Comité Provincial de Investigación Pública (CPIP). A paid policing service managed by a board consisting of party delegates, CPIP was to thwart anti-Republican plots and to arrest individuals involved. In theory they were to be passed to DSG for further investigation; in practice CPIP's internal filtering body, set up to process detainees, was entitled to administer executions. During some 100 days of its existence CPIP was the key law-enforcement agency before a dissolution decree was issued early November 1936, though few units continued to operate some time afterwards. Another new body, by far less important, was Inspección General de Milicias (IGM). Created also in August 1936 it was an army branch, supposed to co-ordinate logistics and financing of party militias, though it operated also its own Sección de Investigación; IGM was dissolved in November 1936. In September 1936 Ministry of Interior set up its own unit designed to co-ordinate militia activities, Milicias de Vigilancia de la Retaguardia (MVR), a hybrid between state policing force and party militias; initially scarcely active, later MVR recruited men from dissolved CPIP and gained momentum; some of its sections became very active before MVR, including the militia units still operational, was dissolved in December 1936. In December