PHOENIX (AP) - An Arizona man has pleaded guilty to murder charges in the fatal stabbing of his 12-year-old half brother and in a deadly attack weeks later on his cellmate in a Phoenix jail.

The plea Thursday spared Andrew Ward the death penalty in the 2014 killings of his half brother, Austin Tapio, and cellmate, Douglas Walker.

Instead, his plea agreement calls for natural life sentences, meaning he won't get a chance at parole.

The case raised questions about whether Walker should have been paired with a dangerous cellmate.

Authorities say Ward told to a 911 operator that he stabbed Tapio because "Honestly I just felt like killing."

Three weeks later, investigators say Ward stabbed Walker with pencils and blocked his breathing passages by jamming a plastic bag down his throat.