An Orem man is in jail tonight, accused of killing his girlfriend's 13-month-old son. Investigators say there is sufficient evidence to prove the man caused enough injuries to the baby to kill him.

The autopsy came back showing the baby suffered from severe internal injuries, including a lacerated stomach and a ruptured bowel. Even though police think the baby's mother's boyfriend caused it all, the mother's own parents don't think so.

David Petterssen will never forget running into the hospital, frantically wondering how his grandson Austin was doing and getting the awful news from his doctor. "When we arrived, we were told that little Austin hasn't made it," he said.

Austin was only 13 months old and in that short time brought his family so much joy. It was a complete shock for them to hear he died. It was another shock altogether to hear that Orem police arrested his mother's boyfriend for it.

Lt. Doug Edwards, with the Orem Police Department, said, "Police officers had noticed on this little baby some unusual bruising on his stomach and back that raised some questions and got investigators involved."

When little Austin's autopsy came back showing he died from severe internal injuries, police arrested 22-year-old Christopher Thunborg and charged him with third degree child abuse homicide.

He was watching Austin Monday night while Austin's mother was at work. Lt. Edwards said, "He offered an explanation about how those bruises got on the baby, about holding him and falling. But that didn't seem to match up with the physical evidence."

Even still, Austin's mother's family doesn't think Thunborg did anything wrong, and they feel terrible he's in jail. "I can't imagine Christopher would ever hurt little Austin," Petterssen said. "We love Christopher and his mom and dad, and his brothers and sisters, and we want them to know that our thoughts and prayers go out to them at this time."

There was another roommate who was at the house while Thunborg was watching Austin. She told police the baby was crying, and she was trying to sleep, so she covered her head with a pillow and doesn't remember anything after falling asleep.