Updated

Two teenage girls face murder charges in the stabbing deaths of one of the girls' grandparents after police captured the pair Tuesday at a beach house on the Georgia coast.

Holly Ann Harvey (search), 15, and Sandra Ketchum (search), 16, allegedly used a kitchen knife to kill Harvey's grandparents, Carl and Sarah Collier, both 77. Their bodies were found Monday night in their home about 15 miles south of Atlanta, authorities said.

Harvey lived with her grandparents.

"Our investigation indicated they were doing this for freedom and so they could be together," said Fayette County Sheriff Randall Johnson.

Police apprehended the teens at a Tybee Island (search) beach house, Johnson said. They will be returned to the county Wednesday and will be charged, as adults, with murder.

The sheriff said some alleged evidence of the slayings was found in the girls' pickup truck. He would not elaborate.

"They had hooked up with some local boys they had met on the beach last night who had given them shelter," said Lt. Col. Bruce Jordan (search), chief investigator for Fayette County. "They had no clue they (the girls) were involved in a homicide."

The Colliers were stabbed repeatedly with a large knife Monday night, sheriff's Sgt. Belinda McCastle said.

"I knew they had some problems with the granddaughter," Johnson said. He said he believes the killings were premeditated and that the girls had behavior problems.

"I think they just had conflicts with people in general," Johnson said.

Neighbor Neoma Gaskins, who lives two doors down, said the Colliers had lived at the house more than 30 years. She described the grandfather as a retired Delta Air Lines maintenance worker who painted houses, and Sara Collier as a homemaker.

"Sarah had told her Sunday school class they were having trouble with Holly," Gaskins said.

Before the girls' capture, Ketchum's aunt, who identified herself only as Glenda, addressed the teen directly before television cameras:

"We, your family, do not understand your actions in the last 24 hours. Nor do we approve of them," she said. "Please know we love you and hope you make the right decision and face your life and come home."