FAYETTEVILLE, Georgia (AP) -- Police were seeking two 15-year-old girls believed on the run after fatally stabbing the grandparents of one of the teens.

Carl and Sandra Collier, both 77, were stabbed to death at their home Monday night in north Fayette County, about 15 miles south of Atlanta, sheriff's department Lt. Col. Bruce Jordan said.

Murder warrants were issued for the couple's granddaughter, Holly Harvey, and her friend, Sandra Ketchum.

Jordan said the girls might be headed south to Florida or toward the Carolinas.

"The girls are on the run. They're in a panic," Jordan said. "We believe they still have the murder weapon with them."

Harvey had been living with her grandparents, Jordan said.

Jordan said the Colliers were stabbed repeatedly with a large knife. Carl Collier was found in the kitchen, and Sandra Collier was in the basement.

"She put up a pretty good fight," Jordan said, saying Sandra Collier had been stabbed "at least 15 times."