A man slain by a fellow Rikers Island inmate would still be alive if jail officials had moved the attacker into a specialized unit for mentally ill detainees, a lawsuit slated to be filed Monday charges. Artemio Rosa strangled Casey Holloway as the 35-year-old victim sat on a chair in the Anna M. Kross Center on Rikers Island on July 9, 2018. Rosa, 27, “had a history of mental illness and violent behavior,” according to the complaint being filed on behalf of Holloway’s sister, Sheila, in Manhattan Federal Court. Rosa and Holloway were in a “Mental Observation Unit,” Correction Department records show. But Rosa should have been moved to an area with more intensive care called the Program to Accelerate Clinical Effectiveness (PACE), the lawsuit alleges. Lack of Supervision “This tragedy took place not only because of a lack of proper supervision on the day Casey was murdered, but also because of the city’s long running, systemic failure to provide proper care for the mentally ill at Rikers Island,” said Holloway family lawyer Josh Kelner. The de Blasio administration has struggled to open enough of those units to handle the hundreds of inmates with serious mental illness, THE CITY previously reported. Mayor Bill de Blasio vowed to create 12 such units by the end of 2020 — but only six had opened as of April, the lawsuit notes, citing THE CITY’s coverage. Instead, the city has left “nearly all” inmates with serious mental illness in inferior mental observation units, according to the complaint. PACE units have daily counseling and multiple programs, while offering more robust medical care than the Mental Observation units. Staff in the units also strongly encourage inmates to take their medications, and monitor if the meds need to be adjusted. Holloway, who was asthmatic, struggled to breathe and collapsed after a guard yanked Rosa off him, according to Correction Department records. Rosa pleaded guilty to strangulation and was sentenced to eight years in prison. He was in jail facing criminal mischief and assault charges at the time of the attack. Holloway, an aspiring music producer, was homeless for several years, according to his family. He was raised in Chicago by a grandmother and an aunt after his mother died when he was young. He was in jail facing robbery charges. Inmate advocates argue that seriously mentally ill inmates should be placed in medical facilities instead of jail. Approximately 1,100 incarcerated people — 16% of the jail population — were diagnosed with serious mental illness as of March, according to Correctional Health Services, a division of the city’s Health + Hospitals. That share has risen in recent years as the overall jail population has declined. THE CITY reported in March the de Blasio administration intends to develop facilities outside of Rikers and the city’s other jails that offer specialty care for the mentally ill. Details of that plan, including the location and number of beds, have not been finalized.