Nathan Sloop, 34, is having a preliminary hearing for the murder, after Ethan Stacy, 4, was found dead in a shallow grave by the mountains in 2010.
Sloop admitted to beating the boys face in with a hammer so he was not recognizable. He also sprinkled dog food over his buried body.
Mother Stephanie Sloop, 30, is also accused of murdering the boy but it is not clear if prosecutors will seek the death penalty for her, as they are for Nathan.
Text messages were revealed on Wednesday, detailing the disturbing thought processes the two had while the boy was alive.
"I told you we had a pit bull on our hands, but they learn," Nathan texted to Stephanie.
"Just like Mommy, LOL," she said.
"I told you we had to break his ego," he replied.
"He is broke that's for sure," she said a couple of days later.
He then said they had to "figure out how to keep him in his room."
They are both being charged for capital murder.
Nathan is also facing charges of obstructing justice and intentionally inflicting serious injury on a child, and desecration of a dead body.
Prosecutor David Cole said Nathan's "reckless indifference to human life" caused the boy's death.
Cole said Ethan was scalded, beaten, over-medicated and not given medical care.
Though Nathan was not on stand yesterday, the court played recorded phone calls, taped police interviews and read transcripts of interviews.
In one of the tapes, Nathan told police that he slapped the child repeatedly and often made him stand with his nose against the wall. He also admitted to pushing him into scalding water.
He then described a time when Stephanie placed human feces in his mouth. He said they never took him to the hospital when he was sick.
"[Ethan] had seen things and heard things that a four-year-old boy should never see or hear," he said.
They also played a phone call Nathan made from jail to his mother. In it, he said that Ethan was "poison" and was the reason for his failed relationship with Stephanie.
The court then played a video of Ethan saying that he was not scared of Nathan anymore and that he was "having fun."
Nathan is heard asking Ethan if he wanted to stay in Utah with him and his mother, or live with his father in Virginia.
"Where do you want to live?" he asked.
As he cried and wheezed, Ethan said, "My mom, my mom, my mom."
Nathan has pleaded not guilty to the charges. His attorney, Richard Mauro, said they will only consider a plea deal after they see what the prosecution presents as evidence.
Mauro's plan is to challenge the constitutionality of the death penalty.
Stephanie is due in court in April.
Ethan died after he came back to live with his mother for the summer in Utah. It was only 10 days after he arrived that the couple reported him missing, but Nathan later admitted they buried his body near a ski resort.
During the days he was with them, he suffered "severe abuse" including beatings, burning, drugging, isolating, and starving.