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Prosecuting an Ohio family of four arrested in the gruesome slayings of eight people from another family could take years to conclude, a county prosecutor said as the first break in the more than two-year-old case was announced.

Tuesday’s announcement marked the culmination of a massive investigative effort that began after seven adults and a teenage boy were found shot in the head at four separate homes in April 2016. The killings terrified local residents and spawned rumors that it was a drug hit, but prosecutors suggested the attack had stemmed from a custody dispute.

The investigation is one of the most complicated and extensive in state history, with enormous numbers of witnesses and a huge amount of evidence, said Pike County Prosecutor Rob Junk.

“There is a lot of hard work ahead of us. I cannot emphasize that enough. An indictment is only the beginning of the case,” Junk said Tuesday, adding that the case may have to be moved from Pike County because of the pre-trial publicity.

Ohio Attorney General Mike DeWine said a grand jury indicted the four members of the Wagner family on aggravated murder charges. Police arrested George “Billy” Wagner III, 47; his wife, 48-year-old Angela Wagner; and his sons George Wagner, 27, and Edward “Jake” Wagner, 26. They could be sentenced to death if convicted, DeWine said.

DeWine gave scant detail about why the victims were killed, but said the custody of a young child played a role. Edward Wagner was the long-time former boyfriend of 19-year-old Hanna Rhoden, one of the eight victims, and shared custody of their daughter at the time of the massacre.

Edward Wagner was also charged with unlawful sexual conduct with a minor for having sexual contact with Rhoden when she was 15 years old and he was 20 years old, DeWine’s office said.

The Wagner family lived near the scenes of the killings about 60 miles (97 kilometers) south of Columbus.

The mothers of Angela Wagner and George Wagner also were arrested in Ohio and charged with misleading investigators.

Both Edward Wagner and Angela Wagner previously told the Cincinnati Enquirer that they were not involved in the killings.

Angela Wagner said in an email to the newspaper that what happened was devastating and Hanna Rhoden was like a daughter to her. Wagner also told The Enquirer that her husband, George, and Christopher Rhoden Sr. were more like brothers than friends.

John Clark, a lawyer who has been representing the Wagners, has said previously that four of the Wagner family members provided laptops, phones and DNA samples to investigators, and agreed to be interviewed about the slayings.

“We look forward to the day when the true culprits will be discovered and brought to justice for this terrible tragedy,” Clark said in a statement Tuesday.

The victims were identified as 40-year-old Christopher Rhoden Sr.; his ex-wife, 37-year-old Dana Rhoden; their three children, 20-year-old Clarence “Frankie” Rhoden, 16-year-old Christopher Jr., and 19-year-old Hanna; Clarence Rhoden’s fiancée, 20-year-old Hannah Gilley; Christopher Rhoden Sr.’s brother, 44-year-old Kenneth Rhoden; and a cousin, 38-year-old Gary Rhoden. Hanna Rhoden’s days-old baby girl, another baby and a young child were unharmed.