Oklahoma prosecutors charged two people on Friday for the fatal shooting of a 17-year-old girl in what is reportedly a case of ‘payback’ over a sexually transmitted disease.

Andrew Hall, 30, and Cheyenne Blalock, 17, were charged with first-degree murder in the fatal shooting of Kirstan Patterson, 17, according to court documents.

Patterson’s mother and stepfather reported the teenager missing on New Year’s Day and her body was found hours later near the Spring Creek boat dock on the Neosho River in Mayes County, with a gunshot wound to the head, deputies said.

The Mayes County Sheriff’s Office arrested Hall and Blalock later that day and they are being held on a $1 million bond. Their next court appearances are set for Jan. 9.

“Blalock said that Andrew Hall, her boyfriend, had talked about killing Kirstan before because of a transmission of a sexually transmitted disease and wanted to ‘payback,’” a Mayes County Sheriff’s Office detective wrote in a probable cause affidavit.

Interviews with both Hall and Blalock revealed that Hall had discussed several ways of killing Patterson, according to investigators.

Sheriff Mike Reed said the two suspects and the victim all lived in Chouteau and previously knew each other. Blalock and Patterson reportedly attended the same school in the Oklahoma town.

Authorities said that Blalock hid under a blanket in the back of Hall’s car on New Year’s Day when he picked up Patterson and drove to the Spring Creek Recreation Area.

Hall allegedly told detectives that Blalock had knives on her and thought she “was only going to physically assault” Patterson, according to the affidavit, and that he complied with her demands because he feared that she would hurt him.

Deputies said that both Hall and Blalock claim the other procured a rifle from Hall’s truck and shot Patterson in the head. Blalock told detectives that she did not see the shooting but heard two shots, and subsequently touched Patterson’s body to confirm she was dead.

“Blalock said Hall poured bleach on the body in some effort to destroy evidence, and then Hall moved the body into the water,” the affidavit reads. Both suspects reportedly told investigators that Hall hid the rifle under his bed at his Chouteau residence.

Mayes County Sheriff’s Office Maj. Rod Howell said Blalock and Hall have pointed the blame at one another for the homicide.

“Our heart goes out to the family,” said Howell. “I’ve met with them, visited with them in depth, and I just can’t understand what they’re going through.” “I’ve got kids, and I just couldn’t even fathom,” he added.