A Phoenix man who reportedly told police he killed his 12-year-old half brother last month because he "just felt like killing" is now accused of fatally stabbing a cellmate, authorities said Thursday.

Andrew Ward, 27, was arrested on suspicion of first-degree murder in the Wednesday night killing of cellmate Douglas Walker, 33, in a Maricopa County jail in Phoenix, the Sheriff's Office said in a statement.

Walker was stabbed in the eyes with a golf pencil, the statement said. His throat was cut with a plastic playing card, he was beaten, his head was smeared with peanut butter, and paramedics later discovered that his breathing passages were obstructed by a plastic bag, the office said.

Officers discovered Walker's injuries when they went to the locked cell after inmates said there was a fight, the office said.

Ward immediately admitted to sheriff's detectives that he had choked and beaten Walker, the office's statement said. "Ward told sheriff's detectives that he had no regrets for the attack."

Ward previously pleaded not guilty in the March 12 killing of Austin Tapio, his half brother. Ward was arrested after calling 911 from a convenience store near his family's home. The boy had multiple stab wounds.

Police said when asked why he killed the boy, Ward said, "Honestly, I just felt like killing."

Marci Kratter, Ward's defense lawyer in the March killing did not immediately respond to requests for comment Thursday.

The Sheriff's Office said Ward and Walker had been housed together the past three weeks in the Lower Buckeye Jail.

"Prior to the March arrest, Ward had been in jail on 11 different occasions since 2006 with no major disciplinary problems or notable institutional history," the office's statement said.

According to online court records, Walker was awaiting an April 11 sentencing after he pleaded guilty last month to armed robbery. He had been in custody since November, the Sheriff's Office said.

In mid-January, an inmate at the same county jail was fatally beaten and stabbed with a small pencil by his cellmate.

The Sheriff's Office said 20-year-old Nike Black is charged with killing 50-year-old John Klatt and that the two had no known previous conflicts.

Klatt was awaiting trial on charges of sexual exploitation of a minor, while Black faced charges of domestic violence, assault and criminal trespassing. Black now also faces a murder charge.

___

Associated Press reporter Jacques Billeaud contributed.