Jennifer Pierce, News 9

OKLAHOMA CITY -- Police say Crystian Rivera confessed to shaking his baby sister to death, now he's one of the youngest inmates at the Oklahoma County jail.

The 13-year-old is accused of first degree murder. He is being treated as an adult, but he's not allowed to stay in a jail cell with an adult.

One week ago, Crystian Rivera was your typical 13-year-old at home playing video games. But on that day, police say he was watching his 9-month-old sister, while their parents were at work.

Detectives say the baby distracted Rivera from his game, he told police he got angry and confessed to shaking his sister.

Three days later she died at the hospital from a severe brain injury, and Rivera was taken to the Oklahoma County jail.

We went behind the doors where Rivera is being held, with 26 other juveniles charged with serious offenses. He's locked up in cell number one with one other person. Jail officials say he is checked on every 30 minutes.

Rivera was arrested just days before school started. He would have been an eighth grader at Mayfield Middle School. But now, his schooling will happen behind bars.

"We have a contract with the Oklahoma City public schools," said Mark Myers, Oklahoma County Sheriff's Department spokesman. "And they provide teachers that come out and teach our juvenile inmates."

Rivera is being held without bond. The Oklahoma County District Attorney's office has not been presented with charges yet.

Under state law, Rivera will undergo a youthful offender study to determine if he can be rehabilitated. If that is the case, he would be released when he is 18 and half years old. If not, he could be sentenced to life in prison. He is too young to get the death penalty.