Mr. Stanbro, however, was accused of assault and after he left the hospital was put in solitary confinement.
At Clinton Correctional Facility, near the Canadian border, guards kicked and punched a handcuffed man, breaking his rib.
In all three cases, the staff members filed false reports to cover up the assaults, court records show, and faced no discipline.
The Marshall Project obtained disciplinary data on more than 290 cases in which the corrections department tried to fire guards or supervisors accused of abusing prisoners.
In nearly three-quarters of those cases, the agency also accused the officers of covering up misconduct, often by acting in concert.