Lori Vallow, already charged in the deaths of her two children, has been indicted in connection with the 2019 killing of her fourth husband, Arizona prosecutors said Tuesday.
Vallow is charged with one count of conspiracy to commit first degree murder, the Maricopa County Attorney's Office said in a statement. A grand jury charged her on Thursday.
Vallow is accused of agreeing with her brother, Alex Cox, to kill Vallow's husband, Charles Vallow, in 2019. Before Charles Vallow died, he had filed for divorce.
Cox called 911 on July 11, 2019, and said he fatally shot Charles Vallow, the Maricopa County Attorney's Office said. He claimed self-defense and was never charged. Cox died in December of 2019 of what the medical examiner ruled was natural causes involving a blood clot.
In May, Lori Vallow and her husband Chad Daybell were charged in Idaho with murdering her two kids, who were last seen in September 2019.
Joshua "JJ" Vallow and Tylee Ryan were 7 and 16 respectively when they disappeared.
Maricopa County Attorney Allister Adel said in Tuesday's statement that "complex, difficult cases of this nature take time to properly investigate and solve."
In addition to the charges relating to the children, Daybell has been charged in Idaho with first-degree murder in the death of his wife, Tammy Daybell.
She died in October of 2019 at the age of 49. Lori Vallow and Chad Daybell married weeks later. Tammy Daybell's death was initially ruled natural but was later ruled as a homicide, according to indictments released in May.
Daybell is also charged with insurance fraud related to her death. Vallow has been charged with conspiracy in her death, according to prosecutors.
An e-mailed request for comment from an attorney who represents Vallow in the Idaho cases was not immediately returned Tuesday evening.
Vallow earlier this month was ordered treated at a mental health facility after being found unfit to stand trial for separate concealment of evidence charges she faces.
Daybell is a self-published author who has written more than two dozen books about near-death and doomsday events, and multiple people close to Vallow have raised red flags about her doomsday beliefs and mental state.
The two children were last seen alive in September of 2019, and Vallow and Daybell had never reported the children missing and did not cooperate with investigators before they fled the state, police in Rexburg, Idaho, have said.
This story first appeared on NBCNews.com.