A pair of mental health experts have found that Chelsea Thornton was legally insane when she shot her 3-year-old son and drowned her 4-year-old daughter in the bathtub of their Gert Town apartment nearly two years ago.

Forensic psychiatrists Dr. Sarah Deland and Dr. James McConville said Thornton knew she was breaking the law but thought it best to kill her children anyway.

Thornton, 25, has a lengthy history of mental illness, having been diagnosed at various times with bipolar disorder and schizophrenia, with psychotic episodes, as well as depression. Hospital records showed she had been off her medication for several months before the killings.

“She was tired of seeing her kids suffer. She felt they were poor and things were not going to get better and she didn’t want them to go from pillar to post,” McConville testified at a hearing Thursday. “It was almost as if she felt this was some sort of mercy killing. … She did feel that what she was doing was the right thing to do.”

Both psychiatrists were hired by Thornton’s defense attorney, Lionel “Lon” Burns, in a bid to support Thornton’s plea of not guilty by reason of insanity to a pair of first-degree murder charges that a grand jury handed up in January 2013.

The doctors submitted a 34-page report to Orleans Parish Criminal District Court Judge Robin Pittman, detailing their findings from two separate interviews with Thornton, weeks after the killings and again on Aug. 28. They also interviewed relatives and reviewed videotapes from cameras that caught Thornton at a day care center and while she rode the bus that day.

Last year, Thornton was deemed competent to stand trial after spending months in a state hospital. The issue on Thursday was whether she knew right from wrong when she shot her son Kendall in the head and pushed him underwater in the bathtub, then drowned her daughter Kelsey in the same tub when the gun jammed.

Thornton was despondent the day she killed them, McConville testified. She never tried to hide what she did and started to tell police but then got scared. After a trip to the hospital, she confessed to police, following the discovery of the bodies by a relative.

Thornton was “almost getting catatonic on that day,” Deland testified. “She feared for their future and thought going to heaven was the best thing for them.”

She hugged her children and told them she loved them first, McConville said, and then later tried haphazardly to kill herself. She dunked her head in water, then tried to cut her wrists using a dull knife, he said.

There was no indication that Thornton was intoxicated at the time, the psychiatrist said.

The testimony and report have no bearing on the ability of District Attorney Leon Cannizzaro’s office to move forward with its case against Thornton. Ultimately it’s up to a jury to decide on Thornton’s sanity at the time of the offense. Pittman said she couldn’t rule on the issue unless Thornton waived a jury and requested a judge trial.

A spokesman for Cannizzaro’s office, Christopher Bowman, said the office still may seek the death penalty for Thornton.

“It is presently a capital case,” he said.

Burns, who is running to unseat Cannizzaro as district attorney, argued that the experts’ testimony should “take death off the table. All that’s out the window.”

With the expert opinions in hand, he said, he’ll seek to have Thornton’s confession thrown out of the case at a hearing slated for next month.

“Obviously, if she was insane at the time of the offense, she was insane at the time of the confession,” Burns said.

Thornton confessed shortly after the killings.

She remains jailed without bond in Orleans Parish Prison. She sat quietly in orange jail scrubs at the defense table on Thursday as the doctors recounted her state on the day of the slayings.

“She said, ‘I’m depressed hearing this,’ ” Burns said of her reaction to the testimony.

Follow John Simerman on Twitter, @johnsimerman.