Disturbing new details emerged last week in a California court in the year-old case of a mother charged with killing her son and daughter just days after her ex-husband was granted full custody of the children in Cobb County.

Marilyn Kay Edge was arrested in September 2013, and charged with two counts of murder after 13-year-old Jaelen and his 10-year-old sister, Faith, were found dead in a motel room in Santa Ana, Calif.

Police allege that Edge poisoned, then suffocated and drowned the children, who were both found in the bathtub of the motel room.

The Orange County Register reported this week that according to Orange County Grand Jury testimony made public last week, Edge methodically planned the murders as she drove her children from Cobb County to Arizona – where she had moved a year earlier after her ex-husband was granted visitation rights – and on to the California coast.

“She wanted the children to have a nice day, a nice time,” Santa Ana police Det. Eddie Nunez told the grand jury. “They liked the beach, so she took them to Huntington Beach. And then she was going to take them to dinner and then she was going to kill the children.”

According to the Register, a Cobb judge ordered Edge to turn the children over to their father three days before they were killed.

Instead, she “left the courthouse in a car that she borrowed from her parents and drove toward Arizona,” Orange County Deputy District Attorney Larry Yellin told the grand jury. “She decided that rather than do what the court had ordered, she was going to kill her children and herself.”

Yellin told the grand jury that on the way back to Arizona, Edge bought packets of over-the-counter sleeping pills at different stores, and shopped for more medicine in Arizona before traveling on to California.

But Edge had a hard time getting the children to take the sleeping pills when the three got back to the Santa Ana Hampton Inn & Suites after a day at the beach and dinner.

“She had crushed them up and put them in liquid,” Yellin told the grand jury, according to the Register. “It was juice or soda or something like that, but it had made the taste unappealing and so the children were resistant to drinking it.

“But ultimately, she was able to get enough of it in them to where they lost control of their abilities to fight what was coming.”

Yellin said Edge then decided to drown the children, and put them in a tub full of water.

Nunez, the Santa Ana police detective, told the grand jury that Edge told him Jaelen stayed in the tub, but Faith got out and laid down on the couch, according to the Register.

Nunez said Edge grabbed a pillow, “put it over Jaelen’s face and held him under the water until he stopped kicking and he was dead.”

Edge then gave Faith more of the medicine, according to Nunez.

“She tried to get her back in the bathtub, and what she did is she lied to her and told her there was a fire in the building and that they needed to go and get in the bathtub and get under the water for safety reasons,” Nunez testified. “But that didn’t work. She ends up getting the pillow that was in the bathtub and puts the pillow over Faith. When she was on the couch, she smothered her.”

As previously reported by The Atlanta Journal-Constitution, Edge then attempted to commit suicide, crashing her car into an electrical box outside a shopping center, and trying to choke herself with a belt or rope as rescuers worked to free her from the car.

Edge is being held in the Orange County Jail without bond. The charges carry a maximum penalty of death, but prosecutors have not said if they will seek the death penalty.