"Deinstitutionalization and Mass Murders
Could deinstitutionalization have contributed to the rise of mass shootings? Since 1976, there has been an average of 20 mass murders a year. J. Reid Meloy, Ph.D., is a forensic psychologist who studied them. He found that mass murderers suffer mental illnesses that range from chronic psychotic disturbances and schizophrenia to paranoid disorders. They have the paranoid, narcissistic and schizoid traits of personality disorders.
These were not normal people who simply "snapped." Instead, they suffered for years from untreated or poorly treated mental illness. Most planned the shooting for years. Meloy argues that behavioral threat assessments are available and that these are our best hope of prevention. (Source: "Seven Myths of Mass Murder," Psychology Today, April 21, 2014.)"
Was this guy’s behavior certifiable before the killings?
No. Then deinstitutionalizing has no bearing on it.
That individual had no history of mental illness, said some early reports. May be right, may be wrong.