On her visit to Democratic Kampuchea in 1978, Elizabeth Becker asked one of the top members of the Communist Party of Kampuchea (CPK) ‘Standing Committee’; Ieng Sary, whether her and the small delegation she was travelling with could see the prisons of the country. He replied that ‘there were no prisons in Democratic Kampuchea.’

This, as most are aware, was not quite true. Ieng Sary, at the time foreign minister for the now defunct regime (and who died on trial for crimes against humanity in 2013) was telling Becker that there were no prisons in this country, despite their conversation probably taking place less than a few kilometres from the high school that was turned into an interrogation and execution centre that you reference in your question. This institution, codenamed S-21, would have been processing confessions and torturing its inmates as he uttered those words, while thousands of those who had already been sent there, now lay dead in a mass grave about twenty minutes drive away from Phnom Penh.

You could also say, as many survivors of the regime did, that the whole country was turned into ‘a prison without walls.’

To answer your question, I will detail the ‘prison network’ of DK, as well as relate the main differences between the ‘provincial prisons’ and the centre of the CPK’s security network, S-21.

But first, a note on how the ‘Khmer Rouge’ functioned in relation to those who were members of the army. This army was under the direction of the CPK, which was itself comprised of a ‘standing committee’, where a handful of people made all the decisions in a highly centralised system. The army itself was divided into those that were involved in combat and those who comprised the Khmer Rouge that worked at all other levels. The majority of low-level cadres not involved in combat would staff the security centres, but the entirety of the army was utilised in defending the regime from ‘enemies’, external ones – but primarily those within the country.

The army, therefore, was essentially just tasked with carrying out the will of the CPK, a regime obsessed with ‘sweeping clean enemies’, and one method of doing this was by setting up security centres around Cambodia.

Meng-Try Ea in The Chain of Terror, suggests that there were five categories of security centre. The lowest were small prisons that focused on localised areas, usually only detaining a few inmates who would be generally set free after a short period. Some prisoners would be sent ‘up the chain’ to the next category, the ‘district re-education and regional security centres’. Prisoners sent here would be detained, interrogated and executed and included members of the former Lon Nol regime, those who had stolen something, ran away, spoke ill of the current regime or cadre who had been accused of betraying the revolution.

Above this level were zone security centres. DK was divided into several ‘zones’ that generally overlapped with the ‘districts’ that had been in place prior to the Khmer Rouge coming to power (like states within a country). This category of security centre was large and held a thousand or more prisoners. Primarily Khmer Rouge soldiers and cadre were sent here –and their families– and these places served as both hard labour and execution sites.

Above all these categories, or perhaps at the centre, was S-21. The most important prisoners were sent here, including former members of the standing committee like Vorn Vet.

There were more than 150 of these security centres around Democratic Kampuchea, but they varied widely in their size, purpose and importance. Some were temporarily set up. I’ve visited one in Prey Veng province, a school that was used to detain soldiers caught up in the east zone purges of 1977-8, before they were executed and buried in a mass grave behind one of the buildings.

People could be moved up, and generally were, but some were also sent ‘down’, to work in hard labour camps or sent to re-education centres. This may have been as high as 20 or 30 percent in the smaller prisons, but the higher level of centre you were in would reduce that percentage eventually to zero, famously only a handful of people sent to S-21 would survive that sentence. After 1976, as the regime became more obsessed with purging internal enemies, the chances of being released at a district or regional centre also became nearly impossible.

One major difference between S-21 and the others was the focus on prisoner autobiographies. Because those sent to Tuol Sleng were considered to be important enemies of the regime, and because it was thought that none would have acted alone, it was imperative to comb through their confessions and produce huge statements of their guilt – often encouraging prisoners to produce the names of many accomplices as they were subjected to torture. In the provincial ‘prisons’, this was not a focus. Interrogations were different, prisoners never wrote their own biographies but were instead interrogated by just a three-person team, one asking questions, one taking notes and one beating the prisoners. Beatings were common, as was the use of plastic bags, but no ‘high level’ torture like that seen in the exhibits of Tuol Sleng.

Henri Locard suggests that living conditions in the provincial prisons, ‘were even worse than 21’, since the inmates had no right to wash themselves. He said that one had to be careful about generalising, as we’ve seen there were more than 150 prisons and he described it as ‘chaos’. Insects and parasites were more of an issue in these regional prisons, exacerbated by the filth and treatment of those detained. He said that food was very simple, all over Cambodia, clear rice soup twice a day and a very small amount. Usually after three/four weeks people would not survive. This was better at S-21 since prisoners could survive several months. The average lifespan was about three weeks according to the historian’s testimony at the Khmer Rouge tribunal.