Medical teams on Monday finished the autopsies of eight family members shot and killed in a total of four different homes in southern Ohio, as officials revealed the investigation had uncovered three marijuana growing operations.

“This was a preplanned execution of eight individuals,” Ohio Attorney General Mike 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."

DeWine and Pike County Sheriff Charles Reader did not immediately release the results of the autopsies. The attorney general had prevously said each relative apparently was shot in the head, and that none of the shootings appeared to be a suicide.

Most were apparently sleeping when they were killed. Three young children -- including a 4-day-old infant -- were also found unhurt.

“This is not your case where someone got mad at somebody else, shot him, there’s a witness, two witnesses. It’s a very, very different kind of case,” DeWine added, saying it wasn't clear whether drugs played any role in the shootings.

All the victims were members of the Rhoden family: 40-year-old Christopher Rhoden Sr.; his 16-year-old son, Christopher Rhoden Jr.; 44-year-old Kenneth Rhoden; 38-year-old Gary Rhoden; 37-year-old Dana Rhoden; 20-year-old Clarence "Frankie" Rhoden; 20-year-old Hannah Gilley; and 19-year-old Hanna Rhoden.

DeWine said a force of at least 100 investigators had already received more than 100 tips and conducted more than 50 interviews. Five search warrants had been executed and the four crime scenes had been evaluated and secured. DNA technicians were currently examining 18 pieces of evidence at a state crime lab.

Pike County Sheriff Charles Reader said he advised other members of the “targeted” Rhoden family that they could be in danger and advised them to be armed.

DeWine and Reader both cautioned that the investigation likely would take a long time. “A lot of what is going on here is just basic, old-fashioned police work,” DeWine said.

Pastor Phil Fulton, of the Union Hill Church, described the Rhodens as a close-knit and hardworking family. He said they were previously part of his congregation, though not recently. He said a crisis resource team was at the church to work with the family.

"They're not doing well with this situation at all," Fulton said. "A tragic situation like this ..."

The Rhoden family released a statement through the Ohio Crisis Response Team Saturday, according to Fox 19.

"The Rhoden family would like to thank everyone for all the outpouring of prayers and support for their family. They ask to continue to keep them in your prayers,” the statement read. “They would like to thank all law enforcement from Pike County and surrounding counties for their immediate response. Especially, to Pike County Sheriff Charlie Reader for all his hard work. They would like to thank the Ohio Attorney General Mike DeWine, his staff, BCI agents, all EMS services and first responses.”

The family also urged anyone with information to call 1-855-BCI-OHIO.

The Associated Press contributed to this report.