UTAH STATE PRISON — A man convicted of the high-profile stabbing deaths of his two brothers at their home in West Point when he was just 15 years old is now facing a new criminal charge.

Aza Ray Vidinhar, 22, was charged Thursday in 3rd District Court with assault by a prisoner, a third-degree felony.

On Jan. 12, a 35-year-old inmate at the Utah State Prison was arguing with other inmates. When the argument was over, Vidinhar told the inmate to come into his cell, according to charging documents. But the man refused.

This upset Vidinhar, who then attacked the other inmate, slamming the man’s head into a wall, the charges state.

Vidinhar was captured on a security camera punching the man in face while the other inmate backed away, according to the charges. As the other inmate turned to walk away, Vidinhar is accused of punching him in the back of the head, knocking him to the ground and continuing to punch and kick him.

Vidinhar is already serving a term of 15 years to life in prison for killing his two brothers, Alex and Benjie, ages 10 and 4, inside their West Point home on May 22, 2013, stabbing one of them 88 times and the other 28 times.

Vidinhar was originally ordered to remain in juvenile detention until he turned 21 as part of deal that would have him serving time in both the juvenile and adult systems.

But on Nov. 1, 2014, Vidinhar attacked another inmate with a broom handle while in juvenile detention. He was found to be in violation of the plea agreement and was transferred to the Utah State Prison.

At sentencing, prosecutors described Vidinhar as a person with no empathy or remorse who “has a callous indifference toward life and toward others.” A prosecutor said he had actually planned on killing his brothers earlier because they had the television up too loud.

Defense attorneys, however, painted a picture of a boy with serious mental health issues that went undiagnosed and untreated until his arrest, and whose immaturity and personality disorders made him seem cold because he was incapable of articulating his feelings.