The Idaho Attorney General’s Office has taken over the investigation of doomsday couple Lori Vallow and Chad Daybell—and a document in the case reveals potential charges include conspiracy and murder.

The Fremont County prosecutor requested help from the AG’s office in investigating the death of Daybell’s first wife, according to a letter obtained by East Idaho News. Under the heading of “Defendant/Matter,” the AG listed “Chad Daybell, Lori Daybell/Conspiracy, Murder, Attempted Murder.”

Authorities have not publicly accused the newlyweds—who are tied to two missing children, three mysterious deaths, and several bizarre incidents—of those crimes. Instead, in a separate case, Vallow is being held on charges of child abandonment and contempt of court for failing to produce her children. Daybell, the author of apocalyptic novels, has not been charged with anything.

The pair have been under scrutiny since late November, when police went to their Rexburg home to conduct a welfare check on Vallow’s children from earlier marriages, 17-year-old Tylee and 7-year-old J.J.

The kids were not there, and Vallow allegedly lied about their whereabouts. When police returned to ask more questions, she and Daybell were gone—only to surface in Hawaii in February. Vallow was extradited to Idaho after she ignored a court order to show up in court with Tylee and J.J.

Rexburg police have said they believe the children are in danger. Vallow and Daybell have denied any wrongdoing but have also refused to cooperate with the search for the children—which was recently expanded to include a FBI request for photos and videos from visitors to Yellowstone National Park that might show the family there.

What started as a missing-persons case quickly mushroomed into a larger investigation that focused on the couple’s doomsday-centered religious beliefs and the deaths of their previous spouses.

Vallow’s previous husband, Charles, was shot dead by her brother, Alex Cox, who has since died of unknown causes. Charles was estranged from Vallow at the time and had claimed in a divorce filing that she was “obsessive about near-death experiences” and had threatened to kill him.

Months after Charles Vallow’s death, Daybell’s wife, Tammy, was also dead—and authorities have since exhumed her body to conduct the autopsy that he refused. Weeks after Tammy’s death, Lori and Chad tied the knot—with Lori wearing a wedding ring that reportedly was purchased while Chad was still married.