Story highlights Marijuana not being grown for personal use, official tells CNN

3 marijuana "grow operations" found at site of mass slayings in Ohio, attorney general said

"This was a preplanned execution of eight individuals," Attorney General Mike DeWine said

(CNN) Investigators found three marijuana "grow operations" at rural residences where eight family members were killed in southern Ohio, state Attorney General Mike DeWine said Sunday at a news conference.

Authorities wouldn't say publicly whether they thought the killings were drug-related, but an official with knowledge of the operation told CNN's Nick Valencia: "This operation was not for personal use; it was for something much bigger than that. It was a very sophisticated operation."

The cold-blooded nature of the killings has rattled Piketon, a town of about 2,000 people 90 miles east of Cincinnati.

The victims, who ranged in age from 16 to 44, were methodically shot in the head Friday while sleeping at four residences, including a mother with a 4-day-old infant lying beside her, authorities said. The newborn, along with a 6-month-old and a 3-year-old, survived. The official said the killings happened before dawn.

"This was a preplanned execution of eight individuals," DeWine said. "It was a sophisticated operation and those who carried it out were trying to do everything they could do to hinder the investigation and their prosecution."

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