Chelsea Thornton was not legally sane when she made the decision to shoot and kill her 3-year-old son and drown her 4-year-old daughter, an Orleans Parish judge ruled Friday.

Criminal District Court Judge Robin Pittman delivered her verdict shortly before 11 a.m., bringing an end to a nearly five-year legal saga.

Thornton, who opted for a judge trial rather than take her chances with a jury, was charged in the October 2012 killing of her two young children. Though she confessed to the killings, Thornton's defense hinged on her mental capacity at the time. She has a documented history of mental illness.

Her case was delayed numerous times as medical experts clashed over whether the young mother was legally fit to stand trial and, later, over whether she was sane when she carried out the horrific slayings of her two young children.

Thornton was indicted on two counts of first-degree murder. In June, Orleans Parish District Attorney Leon Cannizzaro's office said it would not seek the death penalty.

Thornton, 28, had entered a dual plea of not guilty and not guilty by reason of insanity. Pittman found her not guilty on two counts of first-degree murder and not guilty on one count of possession with the intent to distribute marijuana.

Thornton will now undergo further evaluation and treatment at a state medical facility. 

Under Louisiana law, people who are found not guilty by reason of insanity and are deemed to remain both mentally ill and dangerous are assigned to inpatient treatment at a state mental hospital or private psychiatric facility.

At some point, a hospital review committee could recommend Thornton's release. A judge would then need to find that she is no longer a danger to herself or others before she could go free.

Throughout the week-long trial, prosecutors presented a long line of expert witnesses including state pathologists, forensic psychologists and psychiatrists, and New Orleans police detectives.

The judge also heard testimony from Thornton’s mother, who tearfully recalled her daughter’s decaying mental state before the killings, and the children’s paternal grandmother, who discovered the bodies of her two grandchildren dead in the bathtub.

Thornton’s last day with her children was retraced, step by step, through witness testimony and taped interviews with NOPD detectives.

On the morning of Oct. 17, 2012, Thornton — a 23-year-old mother of two with aspirations of becoming a nursing assistant — was seen picking up her son, Kendall, and daughter, Kelsey, from their nursery school before taking them back to her rat- and roach-infested Gert Town apartment. Once there, Thornton shot Kendall in the head before undressing Kelsey and drowning her in the bathtub.

In a taped interview with NOPD detectives, Thornton could be heard in gut-wrenching sobs explaining to detectives why and how she killed her children.

The recording started at 6:40 p.m. on Oct. 17, less than two hours after the children’s bodies were discovered.

“(Kendall) was like, ‘You about to shoot me, mommy?’ (I said) ‘Close your eyes, baby.’ And I shot him,” Thornton says. “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.”

After killing her children, Thornton changed her wet clothes — something that prosecutors said was evidence of calculated, sane decision-making — and went to see her on-again, off-again boyfriend, the children's father, in the Lower 9th Ward. 

Surveillance footage showed Thornton taking a bus to a police station in an abortive attempt to confess her crimes. Video also captured her later in the day as she sat in a waiting room at Interim Ĵý Hospital for treatment  for stomach pains. 

While at the hospital, the children's father received notice that Kendall and Kelsey had been found dead in Thornton’s apartment. She then confessed to the killings to a doctor and nurse, and later in a taped confession to police.

Throughout the various confessions, Thornton showed no signs of psychosis or delusions, several prosecution witnesses testified, and appeared to be acting in a way normal and expected of a parent who had just lost her children.

Dr. Michael Blue, a psychiatrist who wrote a report saying Thornton was sane at the time of the killings, described her actions that day as a “normal sign of self-preservation” and said she showed no signs of delusion.

Under questioning by Thornton's defense attorney, Lionel "Lon" Burns, Blue acknowledged that Thornton’s medical records indicated she had suffered from a “profound mental illness” for parts of her life, but he insisted she was not delusional at the time of the killings.

Dr. Rafael Salcedo told the court that Thornton's stated rationale for the killings, that she did not want her children to remain trapped in poverty all their lives, as she had, did not qualify as evidence of insanity.

However, James McConville, another forensic psychiatrist who evaluated Thornton, said he believed she suffered from an “altruistic delusion” — a common condition in cases where mothers kill their children.

“It’s a bizarre thought that she would kill the children to keep them from some future suffering,” he said. “This altruistic delusion is bizarre and it’s hard to understand, but it’s consistent throughout the record.”

McConville concluded that Thornton was actively psychotic at the time. “She suffered from the irrational, delusional thought that her children would actually be better off dead and in heaven,” he said.

During the trial, family members described a young woman who had suffered for years with mental stress and depression. They said Thornton, at various times, has been diagnosed with bipolar disorder and schizophrenia with psychotic episodes, along with depression. 

Under questioning by Burns, Thornton’s mother, Eleanor Chapman, described a series of bizarre incidents that had punctuated her daughter’s life.

For years, she said, her daughter would stay up all night, writing on any surface she could find, and in May 2011, she stood in traffic in the middle of the street.

Chapman had her daughter committed to the state mental hospital in Jackson, and she showed signs of improvement when she took her pills, Chapman said. Often, though, her daughter would refuse to take her medication, and her mental condition would deteriorate, Chapman said.

Sometime between six months and a year before the killings, Thornton's doctors informed her that Medicaid could no longer cover the cost of an injection drug that seemed to help her, Chapman said.

“They said the medicine was like $1,100, $1,200. I said we couldn’t afford that. ... I said, 'Well, Chelsea, we going to just pray.' ... I didn’t know what to do after that,” Chapman said.

After Thornton went off her medication again, she became "erratic," Chapman said. Days before the killings, Chapman threatened to have her daughter committed another time.

"I couldn’t get her to snap back," she said.

Thornton, dressed in a maroon Orleans Parish Prison shirt, did not take the witness stand during the trial.

Family members of Thornton’s packed the courtroom gallery Friday, and some gasped and wept after Pittman delivered her verdict.

Burns, who on Thursday opted to waive his closing arguments, an unusual choice in such a high-profile case, said his client understood the outcome of Friday's verdict. 

"She turned to me and said, 'Thank you, Mr. Burns,' " he said. "That's about the only thing she said throughout the whole trial."

Christopher Bowman, a spokesman for the District Attorney's Office, said it was “very disappointed” by the verdict, which is not appealable.

“The district attorney and the entire office is very concerned about the ability of the court to mandate hospitalization for this defendant and feels that the children whom she killed never really received any justice," Bowman said.

Outside of the courtroom, Thornton's mother said she felt grateful to her daughter's attorney and the judge. 

"I just feel relieved," Chapman said. "It's been horrible. It's like reliving it every day for the last five years."

Thornton's uncle, Robert Harrison, with tears streaming down his cheeks, said the outcome brings a welcome end to his niece's long and painful legal journey. 

"I've known Chelsea from a baby, and she tried to be a good mother. I know she was trying hard," Harrison said. "When the babies left, a piece of us left, too, and a piece of Chelsea is gone."

Thornton's next legal hearing is on Sept. 7. 

Staff writers John Simerman and Matt Sledge contributed to this report. 

Follow Helen Freund on Twitter, @helenfreund.