A judge will decide this week if a 12-year-old boy is guilty of killing his 5-week-old cousin outside a Marietta Target.

The boy's trial is scheduled to start Wednesday afternoon before Cobb County Juvenile Court Judge Gregory Poole, court officials said.

Police arrested the boy July 4 after the baby's mother, Brittany Young, found the infant unresponsive. The mother, 22, told police she left her daughter, Millan Young, in the car with the boy while she ran into the Target.

“The baby got fussy and he tried to comfort the baby in different manners,” Cobb County Police Officer Dennis Ryan told the judge last month.

Paramedics rushed the baby to the hospital, where she died the next day. She had multiple skull fractures, Ryan said.

An autopsy determined the cause of death was blunt force trauma. Police have not released details on what happened inside the car.

The boy's attorney, Derek Wright, could not be immediately reached for comment Monday.

The boy, who is in sixth grade, remains in a halfway house in DeKalb County. He previously lived in Florida, but was staying in Cobb County with his aunt for the summer, his mother, Camille Curtis said.

The Atlanta Journal-Constitution is not naming the boy per court order.