After being arrested on a misdemeanor charge following a family dispute last year, Jose Bautista was unable to post $250 bail and ended up in a jail cell on Rikers Island.

A few days later, he tore his underwear, looped it around his neck and tried to hang himself from the cell’s highest bar. Four correction officers rushed in and cut him down. But instead of notifying medical personnel, they handcuffed Mr. Bautista, forced him to lie face down on the cell floor and began punching him with such force, according to New York City investigators, that he suffered a perforated bowel and needed emergency surgery.

Just a few weeks earlier, Andre Lane was locked in solitary confinement in a Rikers cellblock reserved for inmates with mental illnesses when he became angry at the guards for not giving him his dinner and splashed them with either water or urine. Correction officers handcuffed him to a gurney and transported him to a clinic examination room beyond the range of video cameras where, witnesses say, several guards beat him as members of the medical staff begged for them to stop. The next morning, the walls and cabinets of the examination room were still stained with Mr. Lane’s blood.

The assaults on Mr. Bautista and Mr. Lane were not isolated episodes. Brutal attacks by correction officers on inmates — particularly those with mental health issues — are common occurrences inside Rikers, the country’s second-largest jail, a four-month investigation by The New York Times found.