A 14-year-old South Carolina boy faces two counts of murder in the deaths of his mother and unborn sister she was carrying, authorities said Monday.

Sherryle Terry, 35, who was eight months pregnant, was shot several times in her home on Sunday night. The girl she was carrying also died in the shooting, Darlington County Coroner Todd Hardee said.

The boy was arrested a few hours later at a relative's house after witnesses told police he was the shooter, said Darlington County Chief Deputy Tom Gainey, who would not talk about what the teen said to investigators.

He is charged with two murder counts because the baby could have lived outside the womb, said Prosecutor Jay Hodge, who plans to ask for the teen to be tried as an adult.

The teen also shot his 12-year-old sister in the neck, but she is expected to survive, Gainey said. The boy had not been in trouble with the law before and deputies have no motive for the killings, Gainey said.

"This is the first time we've had any issues with him," Gainey said. "We heard his mom was worried he might be in a gang, but we don't think it had anything to do with this."

The boy is being held in a juvenile jail in Columbia, about 50 miles west of the mother's home near Lamar. He will appear before a Family Court judge Wednesday, and Hodge said he plans to ask that the teen be held until the case is finished.

Authorities did not release the boy's name because of his age and said they did not think he had a lawyer.

A woman answering the phone at Terry's home said Terry's husband and other family members were not around. She refused to give her name or take a message.