Ten people allegedly involved in the brutal beating that ultimately killed inmate Robert Brooks have been charged in connection to the death ... with six of them facing murder charges.

Nicholas Anzalone, David Kingsley, Anthony Farina, Christopher Walrath, Mathew Galliher and an unnamed suspect who hasn't been arraigned yet all face charges of second-degree murder in the violent beating.

Three others -- Michael Mashaw, Michael Fisher and David Walters -- have been charged with manslaughter. Nicholas Gentile has been charged with tampering with physical evidence.

The nine suspects who were arraigned Thursday reportedly pleaded not guilty to the charges. While the 10th suspect was unable to be arraigned today, he is reportedly not a flight risk.

As you know ... the New York State Attorney's Office released brutal body cam footage of the beating at the end of December -- featuring several officers holding Brooks down while others punch, kick and even appear to hit him with shoes.

Brooks -- who was serving a 12-year sentence for first-degree assault -- reportedly had a "use of force" encounter with corrections officers at Marcy Correctional Facility in Upstate New York, according to the state attorney general's office.

He was transported to Utica's Wynn Hospital, about 7 miles away, and died in the early morning hours of December 10.

Several of the officers who were present when the beating occurred had past incidents of allegedly using excessive force against inmates filed against them.