Thomas, 25, has had a history of mental problems.
In 2004, he was arrested for stabbing his wife, her 13-month-old daughter, and their 4-year-old, ripping the hearts out of his victims. He stabbed himself, before confessing to police. He was convicted in the death of the boy.
After the Dec. 9 incident, Thomas was transferred to the East Texas Medical Center's Jester Unit, a prison psychiatric unit.
"He will finally be able to receive the mental health care that we had wanted and begged for from day 1," his lawyer, Bobbie Peterson-Cate, told a local paper. "He is insane and mentally ill. It is exactly the same reason he pulled out the last one."