The deceased, nine of whom were under 35 when they died, were being held as in-patients in assessment and treatment units (ATUs), controversial hospitals considered inappropriate for some of the most vulnerable people in society.

ATUs are in-patient units intended for the short-term assessment, treatment and stabilisation of people with mental health conditions who display challenging behaviour, and those with a learning disability or autism are supposed to be discharged within 18 months into community-based care.