-62 66.6% of all juveniles interviewed reported being physically abused by police officers during police custody (Bulgarian Helsinki Committee, Alternative Report on the Implementation of the UN Convention against Torture and Other Cruel, Inhuman and Degrading Treatment or Punishment: Bulgaria, Sofia, July 2017, pp. 19-20, available at: https://tbinternet.ohchr.org/Treaties/CAT/Shared%20Documents/ BGR/INT_CAT_CSS_BGR_29219_E.pdf, accessed 10 October 2020). Currently, the organizations involved in detention monitoring, including NPMs, rely on three methods – observation, interviewing and analysis of documents. In terms of reliability of the information obtained, of course observation scores high. It provides first-hand information on the detention conditions. The monitor feels them not only with his/her eyes, but also with his/her nose and ears. Observation allows for measurement of spaces, temperature, lightening, or noise levels. On the other hand, we always observe changing conditions at a certain moment. And, of course, monitors would normally not be in a position to observe ill-treatment or other forms of abuse of detainees. Analysis of documents is an important source of information to which the researcher may turn at any point after the visit to a detention facility. It is stable and may be relied on for a variety of purposes – reports, recommendations and even legal action. But in a detention facility, documents are usually produced by the authorities and are rarely selfincriminating. NPMs, unlike international bodies, are in a good position to solicit documents from independent sources at the national level from different types of experts and institutions – medical, sanitary, building, social, labour, etc., and should use this opportunity whenever possible. NPMs are also well-positioned to receive complaints from prisoners. When the particular NPM is under the umbrella of the equality body (e.g. the ombudsperson), complaints of discrimination coming from places for deprivation of liberty may be particularly informative about the treatment of groups and individuals in a situation of vulnerability there. Interviewing is the most common method used by the NPMs. When used properly, it provides a lot of advantages – first-hand information from