The entrance to Rikers Island is seen in New York, Tuesday, May 17, 2011. Dominique Strauss-Kahn, the chief of the International Monetary Fund, spent Monday night at infamous Rikers Island, after he was charged with trying to rape a maid at a New York hotel where he was staying. (AP Photo/Seth Wenig)

A secret internal study at Rikers Island, one of the country's most violent jails, uncovered the disturbing levels of officer brutality against inmates, an overwhelming majority of whom are mentally ill.

The Department of Health-conducted study, which was obtained by the New York Times and is the central focus of a four-month long investigation by the paper, found a staggering 129 inmates were seriously injured by officers over an 11-month long period last year. 77 percent of those beaten were classified as mentally ill.

Following the altercations, no officers were ever formally charged.

“There’s lots of brutality,” Daniel Selling, former Rikers director of mental health services, said. “Horrible brutality.”

The treatment of mentally ill inmates at Rikers, who make up 40 percent of the population at the notoriously violent jail, has been under intense scrutiny in recent months after the Associated Press reported on the deaths of two inmates, one of whom "baked to death" in a 101-degree cell.



In this March 12, 2014, file photo, a picture of Jerome Murdough is held by his mother and sister in the Queens borough of New York. Murdough, a 56-year-old mentally ill inmate at Rikers Island jail, "baked" to death in his overheated cell during one of the coldest recorded winters in city history.

The two cases, coupled with the surge in mentally ill inmates, have prompted New York City officials to call for oversight hearings looking into the violence plaguing the jail.

Following the reports, Mayor Bill de Blasio vowed to lead reforms and appointed Joseph Ponte as the city's new correction commissioner.

In the Times' report published Monday, Ponte admitted Rikers was "deeply troubled" when he took over the post. But he ultimately stopped short of fully acknowledging the widespread use of force against inmates.