Kirby Forensic Psychiatric Center in New York City has long been a place of mystery, with little known about what goes on behind the razor-wire fences. As a result, the state-run facility for the dangerously mentally ill — located on Wards Island in Manhattan — has gone all but unnoticed for decades, despite having held some of the city’s most notorious criminals, including serial killers and cannibals like Daniel Rakowitz, the so-called Butcher of Tompkins Square Park. But recently, employees have been speaking up, painting a picture of what goes on in Kirby’s wards. State officials are planning to close...