Eight members of a rural Ohio family were shot in the head and killed while the shooter or shooters spared the lives of three children who were later found by authorities.
Officers found the bodies of the seven slain adults and a killed 16-year-old male at four locations in Pike County on Friday morning. Most were executed while in bed.
"This is not something that you prepare for," Pike County Sheriff Charles Reader said.
Among the victims was a mother who was fatally shot next to her 4-day-old baby.
"It's heartbreaking," Ohio Attorney General Mike DeWine said. "The one mom was killed in her bed with the 4-day-old right there."
The baby's life was spared along with the lives of two other children, aged 6 months and 3 years old.
State criminal investigators have interviewed more than 30 people and met with about 100 family members and friends of the victims, DeWine said. The FBI has also reached out and offered assistance with the investigation, Reader said.
In a joint statement, DeWine and Reader said the deaths appeared to be "execution-style killings."
The killer or killers responsible were still at large as dozens of investigators from the sheriff's office and the Ohio Attorney General's Office worked multiple scenes Friday.
Police and Ross County sheriff's deputies reportedly detained at least one person in Chillicothe around 6:30 p.m., prompting media reports that authorities had a person of interest in custody.
At a news conference Friday night, however, DeWine said he would not use the term "person of interest," saying instead that the detention was part of several interviews occurring as part of the investigation.
"The investigation will go wherever the facts take us," he said. "Investigations like this can take a while."
Seven of the deceased were found in three Union Hill Road homes in Piketon. The eighth was found within a 10-minute drive from the other victims. The scenes were described as including homes and trailer homes about an hour and 40 minutes outside Dayton, Ohio.
Reader said he suspected the killings were targeted and occurred during the nighttime hours.
The victims were identified as members of the Rhoden family, but officials did not release their specific identities.
"This is a horrible tragedy that has occurred here in Pike County," DeWine said. "We advise Pike County residents not to panic but to be careful."
That warning extended to surviving relatives of the deceased, who were offered protection by the sheriff.
The Columbus Dispatch identified Dana Rhoden, her children, some of her grandchildren and her ex-husband among those killed, citing Pastor Phil Fulton of Union Hill Church. Rhoden used to attend Union Hill Church, according to the paper.
"Dana loved her family. She worked hard," Fulton said. "What a tragic thing, a tragic thing. … We just have to lift this family, this community and this whole country up in prayer."
Officials said they did not have a motive for the killings.
The Ohio Attorney General's Bureau of Criminal Investigation is leading the case.
Pike County is an Appalachian area that has struggled economically. It includes Piketon, where a Cold War-era uranium plant closed in 2001 and is still part of a federal cleanup effort.
The deaths were discovered after a 911 caller said two dead males were inside one of the Union Hill Road addresses. While responding, deputies were flagged down and sent to two other places, where they discovered bodies. The final victim was found hours later at a fourth site.
The deaths prompted a brief precautionary lockdown Friday morning at Peebles High School, which is a few miles from the scenes. By noon, operations at the school were back to normal.
Gov. John Kasich, campaigning in Pennsylvania for his Republican presidential bid, said his office was monitoring the situation in Pike County.