Chelsea Thornton sat silently in an orange prison jumpsuit and bright yellow sandals, staring ahead as her recorded voice streamed across a hushed Orleans Parish courtroom.

Over 18 wrenching minutes, Thornton was heard on tape trying to explain to New Orleans police detectives, through occasional sobs, why and how she had killed her two young children in their rat- and roach-infested Gert Town apartment.

The recording started at 6:40 p.m. on Oct. 17, 2012, less than two hours after their grandmother found 3-year-old Kendall and 4-year-old Kelsey dead in the bathtub.

“(Kendall) was like, ‘You about to shoot me, mommy?’ (I said) ‘Close your eyes, baby.’ And I shot him. But I wanted to shoot Kelsey, too, so neither of them would suffer. But the gun, like, it was broke some type of way. So I just drowned them. He was breathing some type of way, and I didn’t want him to suffer, so I put him in the tub with her.”

Earlier in the interview, conducted in a triage room at Interim LSU Hospital, Thornton had described drowning Kelsey.

“My little girl, so she was like, ‘Mama, please.’ And I kept telling her, ‘I love you. I love you and your brother. I don’t want y’all suffer like this. It’s not how you supposed to live,’ ” she said.

“So I just gave them a hug and a kiss, and I said, ‘I love y’all very much.’ ”

Detective Nijel Baddoo asked if the children struggled as she pushed them underwater.

“They didn’t fight,” she replied. “They just, like, was moving and stuff.”

Two years after the double killing that raised disturbing questions over fissures in the city’s mental health care framework, Thornton’s chilling confession aired in public for the first time, in a hearing about whether a jury should be allowed to hear it in a capital murder case against the 25-year-old mother.

Her attorney, Lionel “Lon” Burns, insisted that the tape proved clearly that Thornton was steeped in mental illness. He argued that detectives had skirted obvious questions of her mental health history to secure a legal confession.

But the hearing came just a week after a pair of forensic psychiatrists hired by the defense reported that Thornton was legally competent when she gave the confession, telling detectives she didn’t want her kids to “go from pillar to post their whole life like I did.”

A disturbingly cogent, if irrational, Thornton told the detectives she had wanted to surrender immediately after the killings but couldn’t muster the strength.

“I felt so bad because that’s the only two I have. And I love them. So I went to the police station and I was going to turn myself in, but I was like, no. I just ain’t know what to do,” she said in the recording.

“How you tell somebody that you killed your children? How you kill your children?”

Criminal District Court Judge Robin Pittman denied the motion to suppress Thornton’s statement to police. Pittman set a March 3 trial date in the case, in which Thornton faces two counts of first-degree murder.

Thornton has pleaded not guilty and not guilty by reason of insanity. District Attorney Leon Cannizzaro has yet to say whether he will seek the death penalty for her.

The same two mental health experts who found she was competent when she confessed had testified last month that Thornton was legally insane at the time of the killings. It ultimately will be up to a jury to decide that question, however.

Thornton, at various times, has been diagnosed with bipolar disorder and schizophrenia with psychotic episodes, along with depression.

She had been given medication but appeared despondent — “almost catatonic,” Dr. Sarah Deland testified — on the day of the killings.

In the police interview, Thornton said she checked the children out of preschool that morning and had planned to go to the hospital for birth control medication but found she had forgotten her Medicaid card at home.

She complained of living in poverty, that her children were sickly — possibly from mold — and that she had gotten fired from a job for failing to show up.

“Have you been thinking about this for a long time?” the detective asked.

“No,” Thornton responded. “I just settled down one day recently, like the other day. I was like, ‘I don’t want y’all to live like this. I want better for y’all. You don’t have nothing.’ ”

Thornton shot her son in the head, she said.

Outside the courtroom, tears welled up in Danette Harrison’s eyes. Harrison, an aunt of Thornton, said it was the first time she’d heard the taped confession.

“She wasn’t herself. That wasn’t Chelsea at all. It was what was going on in her head. Something was wrong,” Harrison said.

Harrison said Thornton needs to be treated, not prosecuted.

“Just the whole thing is too much,” she said. “She shouldn’t be in here.”

Follow John Simerman on Twitter, @johnsimerman.