A 44-year-old Arizona mother has pleaded guilty to murdering her 10-year-old daughter and 13-year-old son in a Santa Ana hotel room after losing custody of the children to her ex-husband.

In what prosecutors called a “horrific” and “tragic” case, Marilyn Kay Edge subdued her two children, Faith and Jaelen, using cough syrup and then smothered and drowned them on Sept. 13, 2013, said Senior Deputy District Attorney Larry Yellin.

Edge pleaded guilty to the murders on Friday in Orange County Superior Court and will be sentenced to life in prison without parole when she returns to court on Jan. 8, Yellin said.

While Edge was eligible for the death penalty, the Orange County District Attorney’s Office decided not to seek the death penalty in this case, Yellin said.

Three days before the murders, prosecutors said Edge lost custody of Faith and Jaelen at a family court hearing in Georgia, where her ex-husband lives. Edge was ordered to hand over custody of the children on Sept. 15, but instead she drove with her children to Arizona and then California under the false pretense that they were going on a family vacation, prosecutors said.

Hours after she killed her children, Edge attempted to commit suicide by driving into an electrical box outside a hardware store in Costa Mesa, prosecutors said. She instead crashed into a protective pole and was arrested by Costa Mesa police.

While officers tried to get her out of the car, they said Edge attempted to strangle herself with an electrical cord. Officers eventually broke a window and forcibly removed her from the vehicle, according to grand jury testimony.

Edge told the police officers that Jaelen and Faith were dead at the Hampton Inn & Suites in Santa Ana.

Dr. Yong-Son Kim, a forensic pathologist, testified to the grand jury that an autopsy revealed Faith died from smothering but also had an elevated level of a drug called diphenhydramine in her system, consistent with an over-the-counter sleep aid.

Jaelen, who also suffered from severe autism, died from a combination of drowning and smothering, Kim said. Police found the children in a bathtub in the hotel room.

Yellin told the grand jurors that Edge had planned the murders and took the children to California for a “good time for their last day.”

“She decided that rather than do what the court had ordered, she was going to kill her children and herself,” he said.

Yellen on Friday said there was no indication that Edge had any form of mental illness.

“She destroyed the two lives of her children, she destroyed her ex-husband’s life, and she destroyed her own life,” Yellen said. “It’s tragic on all sides.”

Contact the writer: kpuente@ocregister.com, 714-834-3773