Cameron Knight and Hannah Sparling, Cincinnati Enquirer, and John Bacon, USA TODAY

The killing of eight people in Ohio last week was "a pre-planned execution," the state's attorney general said Sunday, adding that police found marijuana growing operations at three of the crime scenes.

"They thought this thing through, whoever did it," said Ohio Attorney General Mike DeWine.

He also made it clear that the execution-style murders weren't random or spontaneous.

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“This is not the case where somebody got mad at someone else and shot them and there’s a witness, two witnesses,” he said.

Asked about the number of attackers, DeWine replied, “I don’t know if it’s a bad guy or bad guys. It could be one, two, three, four. I don’t think we know.”

DeWine's office earlier said it had completed collecting evidence at the four homes where the bodies were found near Piketon, 70 miles east of Cincinnati. Gov. John Kasich expressed confidence that authorities would nab the killer or killers, telling CBS News that "justice will be delivered."

The victims were identified as Hannah Gilley, 20, Christopher Rhoden Sr., 40, Christopher Rhoden Jr., 16, Clarence "Frankie" Rhoden, 20, Dana Rhoden, 37, Gary Rhoden, 38, Hanna Rhoden, 19, and Kenneth Rhoden, 44. All were shot in the head, some while in their bed. Three children, including a 4-day-old, survived the ordeal.

Pike County Sheriff Charles Reader on Sunday said law enforcement personnel were familiar with the family, but noted: “We have a small county. We are familiar with most people.”

Reader added, “I have never been involved with that family in a criminal nature, and I have been in law enforcement locally for 20 years.”

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Scioto Valley Local School District Superintendent Todd Burkitt said every school district in Pike County committed to send counselors to Piketon High on Monday. They’ll stay as long as students need.

“We don’t have all the answers for this,” Burkitt said. “It’s by far the worst part of the job, when something happens to a kid. None of it makes sense.”

Restaurateur Jeff Ruby, owner of steakhouses in Cincinnati, Columbus and Louisville, Ky., offered a $25,000 reward for information leading to arrests. DeWine said dozens of interviews have been conducted, but no arrests had been made. DeWine said the killer or killers apparently targeted the family, lessening the immediate danger to the public.

"There's blood all over the house," a woman identified as "Bobby" told police in the initial, frantic 911 call after finding two of the bodies Friday morning.

"I think they are both dead," she said, sobbing. "It looks like some(one) beat the crap out of them, and I came in and they were laying on the floor."

Friends and family were struggling with the shock of the loss. Brittany Pettit, 15, was a freshman classmate of Christopher Rhoden Jr., the youngest victim, since first grade. She said they were in the same American government class at Piketon High, and they shared lunch and a study hall.

She said she'll miss his humor.

“He knew what to say to me, and he was always there for me," she said. "Chris is just an awesome person."

Twenty miles south of Piketon, Big Bear Lake Family Resort owner Robin Waddell has known the Rhoden family for decades, ever since Christopher Sr. started working at the resort — building decks or roofs, excavating, whatever needed done.

Waddell would hire the elder Chris Rhoden whenever he needed construction. He was good, Waddell said. He was reliable. He was a friend.

“It’s devastating that something like this could happen,” Waddell said. “And we don’t know what happened.”

Contributing: Greg Toppo, USA TODAY