An Oklahoma man has been charged with the death of his 4-month-old son after doctors found the child had skull fractures and died from blunt force trauma.

Duwuan Betancourt, 36, explained the injuries by telling detectives the infant rolled off the couch onto a soft foam mat a few days earlier and that he often fell over backwards while sitting on the mat, KWTV reported.

The baby, Quinn Betancourt, was brought to the hospital on March 5 and pronounced dead there. His father called 911 just before 4:30 p.m. that day. He said he’d put the boy into a swing for a nap at 12:30 and then forgot about him until 3:45, when he found the baby cold and not breathing.

More than 30 minutes later, he texted his wife, but only typed her name, then called 911 five minutes later.

At the hospital, Betancourt said, “It’s all my fault,” court documents say.

The autopsy revealed that the baby “suffered from injuries consistent with child abuse,” Oklahoma City Police Sgt. Dillon Quirk said. A doctor said the injuries would have occured from the baby being slammed “on a hard surface.”

“The baby would have died within five minutes of sustaining injuries such as these,” the doctor said.

Betancourt was charged with murder and is being held on a $5 million bond.

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[Featured image: Duwuan Betancourt/Oklahoma City Police Department]