PROVO — There were tears almost from the start of the trial Thursday of an Orem man charged with killing Austin Pettersson, the 13-month-old baby of the man's live-in girlfriend.

The boy's mother, Whitney Pettersson, began to sob as prosecutor Randy Kennard described in opening statements how the baby had been struck with such force that his intestines had been torn away from his stomach. The child's body also revealed multiple "suspicious" bruises and other injuries.

Kennard, showing the jury a large photo of the smiling child when he was about 6 months old, said a medical examiner will testify that Austin was the victim of "battered-child syndrome."

Christopher Scott Thunborg, 24, is charged with child-abuse homicide, a second-degree felony, and obstruction of justice, a third-degree felony.

The charges emerged after a March 12, 2008, incident when a man called 911 around 7 a.m. to report his girlfriend's baby was not breathing. Paramedics arrived, and the child was taken to Utah Valley Regional Medical Center, where he was pronounced dead.

Kennard told jurors that Austin's mother had worked a graveyard shift, came home, began to shower and was summoned by Thunborg, who told her Austin was not breathing.

"It was strange to her that he was lying in his bed as if asleep. She immediately picked him up, he was limp — and then begins the nightmare of this case," Kennard said.

There had been other suspicious injuries to the child during the four months the couple lived together — things that Thunborg told the child's mother were accidental, the prosecutor said. One was a situation where the boy had been trying to pull himself up by a computer table where Thunborg was playing computer games and the baby did a "face plant" when he fell onto the surface.

Shortly before Austin died, his mother took him to the doctor for cold symptoms, and the doctor found bruises on the child's ears. This prompted a call to the Division of Child and Family Services, and police began an investigation.

Kennard also said Thunborg at first told police nothing out of the ordinary had happened the night before Austin died. But two days later, during a long interrogation, Thunborg said there had been an accident while he was holding the child. "He stepped on a puppy, he couldn't put his arms out to break his fall, and he fell on the baby full force," Kennard said, adding that medical experts say that would not have caused such injuries.