Newly released bodycam footage appears to show New York corrections officers fatally beating a handcuffed inmate who died the following morning.

The inmate, 43-year-old Robert Brooks, was pronounced dead on 10 December, the day after the incident took place at the Marcy Correctional Facility in upstate New York.

Following an internal review, New York Governor Kathy Hochul ordered the firing of the 13 officers and a prison nurse who were involved in the assault.

The office of New York Attorney General Letitia James has opened an investigation into Brooks' death, and the union that represents state prison workers called the video "incomprehensible".

The footage ? which was released by James on Friday ? shows officers repeatedly striking Brooks in the face and groin while he sits handcuffed on an examination table.

The videos also appear to show a prison officer placing something in Brooks' mouth before striking him, as well as a separate officer hitting him in the stomach with a shoe.

At one point, an officer lifts him by the neck before forcefully putting him on the examination table.

Brooks died the day after the assault. Preliminary examinations determined the cause of death was "asphyxia due to compression of the neck."

It is unclear what initially prompted staff to take him to the prison's medical facility in the first place. The videos do not include audio.

In a filmed statement, James said that she does not "take lightly the release of this video, especially in the middle of the holiday season".

"I release the videos because I have a responsibility and duty to provide the Brooks family, their loved ones, and all New Yorkers with transparency and accountability," she said.

Brooks was serving a 12-year sentence for first-degree assault, according to the Associated Press. He had been transferred to Marcy from the nearby Mohawk Correctional Facility on the same day as the incident.

Elizabeth Mazur, a lawyer representing the Brooks family, said in a statement that the videos show "the horrific and extreme nature of the deadly attack".

"He deserved to live, and everyone else living in Marcy Correctional Facility deserves to know they do not have to live in fear of violence at the hands of prison staff," Ms Mazur said of Brooks.

After the video's release, Hochul ? New York's governor ? said that she was "outraged and horrified" by the incident and felt compelled to hold those involved responsible.

"The state of New York has zero tolerance for individuals who break the law, and I am committed to holding everyone involved fully accountable," she added.

The New York union that represents prison workers said in a statement to local media outlets that what "we witnessed is incomprehensible to say the least and is certainly not reflective of the great work that the vast majority of our membership conducts every day".

The New York chapter of the American Civil Liberties Union, or ACLU, alleged that the beating is "not an isolated incident", however.

"Rather, it highlights a culture of violence and a lack of accountability for wrongdoing by corrections officers that puts the lives of incarcerated New Yorkers at risk," executive director Donna Lieberman said in a statement.

In a report issued last year, the Correctional Association of New York ? an independent watchdog ? found "pervasive allegations of racial discrimination" and "mistreatment by staff", including black inmates being turned away from mess halls for having their hair in cornrows or braids. (BBC, excluding headline)

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