This image, taken in late 1993, shows Utritu, officially known as Lhasa Prison, and Sitru, Tibet Autonomous Region Public Security Bureau Detention Center. Sitru, a Tibetan version of ‘sizhidui’ or ‘Number Four unit’ is a Tibet Autonomous Region-level police detention center just north of Utritu (Lhasa Prison). It has been known for dealing with those thought to pose a risk to state security – as opposed to public security. According to a report by Steven D Marshall for the Tibet Information Network covering political imprisonment in Tibet from 1987-1998, “People held for investigation at Sitru are often suspected of having had contact with ‘foreigners’, especially Tibetans who live in exile, or have travelled abroad themselves, especially to India and Nepal, or are believed to have been involved with collecting or transferring information about human rights.” Sonam Drolkar, a lay nun whose political activism involved being interviewed for a television documentary by a foreign journalist in 1990, nearly died from six months of sustained torture during the ten months she was at Sitru. (Information from ‘Hostile Elements’, cited in main text of the report). Used with kind permission of the photographer.