Eight family members, including a teenager, were shot to death "execution style" in four different homes in southern Ohio, according to local officials.
The victims all belonged to a family named Rhoden, and lived within miles of each other, authorities said. The seven adults and a 16-year-old boy were each shot in the head, according to Ohio Attorney General Mike DeWine.
Some were sleeping when they were killed. The shooter, or shooters, are still at large, officials said.
A new mother sleeping with her four-day-old infant was one of the victims. Two other children - a six-month-old baby and a three-year-old toddler - were also found in the houses. All were unharmed, authorities said.
At a Friday evening press conference, officials said other relatives could be at risk.
"We are advising the family members to be very careful, and take particular precaution," DeWine said. "The individual or individuals who committed this crime are obviously dangerous. We believe they are still at large.
"It's heartbreaking," the attorney general said. "The one mom was killed in her bed with the four-day-old right there."
Seven bodies were found in in three homes along Union Hill Road in Pike County, about 75 miles east of Cincinnati, authorities said.
The eighth victim was found on nearby Dry Fork Road.