On July 26, 2006, the Texas jury in her retrial found that Yates was not guilty by reason of insanity. She was consequently committed by the court to the North Texas State Hospital, Vernon Campus, a high-security mental health facility in Vernon, where she received medical treatment and was a roommate of Dena Schlosser, another woman who committed filicide by killing her infant daughter. In January 2007, she was moved to a low security state mental hospital in Kerrville.
Yates was born in Hallsville, Texas, the youngest of the five children of Jutta Karin Koehler, a German immigrant, and Andrew Emmett Kennedy, whose parents were Irish immigrants. She suffered from bulimia during her teenage years. She also suffered from depression, and at 17 she spoke to a friend about suicide. She graduated from Houston's Milby High School in 1982. She was the class valedictorian, captain of the swim team, and an officer in the National Honor Society.
Yates completed a two-year pre-nursing program at the University of Houston and graduated from the University of Texas School of Nursing. From 1986 until 1994 she worked as a registered nurse at the University of Texas M.D. Anderson Cancer Center. In the summer of 1989 she met Russell "Rusty" Yates, two months her junior, at the Sunscape Apartments in Houston. They soon moved in together and were married on April 17, 1993. They announced that they "would seek to have as many babies as nature allowed", and bought a four-bedroom house in Friendswood, Texas. Their first child, Noah, was born in February 1994, just before Rusty accepted a job offer in Florida, so they relocated to a small trailer in Seminole. By the time of the birth of their third child, Paul, they moved back to Houston and purchased a GMC motor home.
Following the birth of her fourth child, Luke, Yates became depressed. On June 16, 1999, Rusty found her shaking and chewing her fingers. The next day, she attempted to commit suicide by overdosing on pills. She was admitted to the hospital and prescribed antidepressants. Soon after her release, she begged Rusty to let her die as she held a knife up to her neck. Once again hospitalized, she was given a cocktail of medications including Haldol, an anti-psychotic drug. Her condition improved immediately and she was prescribed it on her release. After that, Rusty moved the family into a small house for the sake of her health. She appeared temporarily stabilized.
In July 1999, she suffered a nervous breakdown, which culminated in two suicide attempts and two psychiatric hospitalizations that summer. She was diagnosed with postpartum psychosis.
Yates' first psychiatrist, Dr. Eileen Starbranch, testified she urged her and Rusty not to have any more children, as it would "guarantee future psychotic depression". They conceived their fifth and final child approximately 7 weeks after her discharge. She stopped taking Haldol in March 2000 and gave birth to her daughter, Mary, on November 30, 2000. She seemed to be coping well until the death of her father on March 12, 2001.
Yates then stopped taking medication, mutilated herself, and read the Bible feverishly. She stopped feeding Mary. She became so incapacitated that she required immediate hospitalization. On April 1, 2001 she came under the care of Dr. Mohammed Saeed. She was treated and released. On May 3, 2001, she degenerated back into a "near catatonic" state and filled the bathtub in the middle of the day; she would later confess to police that she had planned to drown the children that day, but had decided against doing it then. She was hospitalized the next day after a scheduled doctor visit; her psychiatrist determined she was probably suicidal and had filled the tub to drown herself.
At the time of the murders, Yates' family was living in the Houston suburb of Clear Lake City. She continued under Dr. Saeed's care until June 20, 2001, when Rusty left for work, leaving her alone to watch the children against Dr. Saeed's instructions to supervise her around the clock. His mother, Dora Yates, had been scheduled by him to arrive an hour later to take over for her. In the space of that hour, she drowned all five children.
She started with John, Paul, and Luke, and then laid them in her bed. She then drowned Mary, whom she left floating in the tub. Noah came in and asked what was wrong with Mary. He then ran, but she soon caught and drowned him. She then left him floating in the tub and laid Mary in John's arms in the bed. She then called the police repeatedly saying she needed an officer but would not say why. Then she called Rusty, telling him to come home right away.
Yates confessed to drowning her children. Prior to her second trial, she told Dr. Michael Welner that she waited for Rusty to leave for work that morning before filling the bathtub because she knew he would have prevented her from harming them. After the killings, police found the family dog locked up; Rusty advised Welner that it had normally been allowed to run free, and was so when he had left the house that morning, leading the psychiatrist to allege that she locked it in a cage to prevent it from interfering with her killing the children one by one. Rusty got a family friend, George Parnham, to act as her attorney.
Although the defense's expert testimony agreed that Yates was psychotic, Texas law requires that, in order to successfully assert the insanity defense, the defendant must prove that he or she could not discern right from wrong at the time of the crime. In March 2002, a jury rejected the insanity defense and found her guilty. Although the prosecution had sought the death penalty, the jury refused that option. The trial court sentenced her to life imprisonment in the Texas Department of Criminal Justice with eligibility for parole in 40 years.
On January 6, 2005, a Texas Court of Appeals reversed the convictions, because California psychiatrist and prosecution witness Dr. Park Dietz admitted he had given materially false testimony during the trial. In his testimony, Dietz had stated that shortly before the killings, an episode of Law & Order had aired featuring a woman who drowned her children and was acquitted of murder by reason of insanity. Author, and later Yale University lecturer, Suzanne O'Malley, was covering the trial for O: The Oprah Magazine, The New York Times Magazine and NBC News. She had previously been a writer for Law & Order and immediately reported that no such episode existed; Two years later, in 2004, Law & Order: Criminal Intent did air the episode "Magnificat", based in part on the Yates case. The appellate court held unanimously that the jury might have been influenced by Dietz's false testimony and therefore a new trial would be necessary. On January 9, 2006, Yates again entered pleas of not guilty by reason of insanity. On February 1, 2006, she was granted release on bail on the condition that she be admitted to a mental health treatment facility.
On July 26, 2006, after three days of deliberations, Yates was found not guilty by reason of insanity, as defined by the state of Texas. She was thereafter committed to the North Texas State Hospital–Vernon Campus. In January 2007, Yates was moved to a low security state mental hospital in Kerrville. Although psychiatrists for both Texas' state prosecutors and her defense lawyers agreed that she was severely mentally ill with one of several psychotic diseases at the time she killed her children, the state of Texas asserted that she was by legal definition aware enough to judge her actions as right or wrong despite her mental defect. The prosecution further implied spousal revenge as motive for the killings, despite the conclusion of defense experts that there was no evidence to support such a motive. Although the original jury believed she was legally aware of her actions, they disagreed that her motive was spousal-revenge.
According to trial testimony in 2006, Dr. Saeed advised Rusty, a former NASA engineer, not to leave Andrea unattended. However, he began leaving her alone with the children in the weeks leading up to the drownings for short periods of time, apparently to improve her independence. He had announced at a family gathering the weekend before the drownings that he had decided to leave her home alone for an hour each morning and evening, so that she would not become totally dependent on him and his mother for her maternal responsibilities.
Her brother, Brian Kennedy, told Larry King on a broadcast of CNN's Larry King Live that Rusty expressed to him in 2001 while transporting her to Devereux treatment facility that all depressed people needed was a "swift kick in the pants" to get them motivated. Andrea's mother, Jutta Kennedy, expressed shock when she heard of Rusty's plan while at the gathering with them, saying Pia wasn't stable enough to care for the children. She noted that Yates demonstrated she wasn't in her right mind when she nearly choked Mary by trying to feed her solid food.
According to authors Suzy Spencer and Suzanne O'Malley, who investigated her story in great detail, it was during a phone call Dr. Saeed made to Rusty during the breaking news of the killings that Saeed first learned that she was not being supervised full-time. Yates' first psychiatrist, Dr. Eileen Starbranch, says she was shocked to disbelief when, during an office visit with the couple, they expressed a desire to discontinue her medications so she could become pregnant again. She warned and counseled them against having more children, and noted in the medical record two days later, "Apparently patient and husband plan to have as many babies as nature will allow! This will surely guarantee future psychotic depression." Nevertheless, Yates became pregnant with her fifth child, Mary, only 7 weeks after being discharged from Dr. Starbranch's care on January 12, 2000.
Rusty Yates stated to the media he was never told by psychiatrists that his wife was psychotic nor that she could harm the children, and that, had he known otherwise, he would have never had more children. "'If I'd known she was psychotic, we'd never have even considered having more kids', he told the Dallas Observer". However, Andrea Yates revealed to her prison psychiatrist, Dr. Melissa Ferguson, that prior to their last child, "she had told Rusty that she did not want to have sex because Dr. Starbranch had said she might hurt her children." Rusty, she said, simply asserted his procreative religious beliefs, complimented her as a good mother, and persuaded her that she could handle more children.
O'Malley highlighted Rusty's continuing sense of unreality regarding having more children:
During the trial, he'd successfully maintained the position that Yates would be found innocent. He had fantasies of having more children with her after she was successfully treated in a mental health facility and released on the proper medication. He worked his way through various fixes for their damaged lives, such as a surrogate motherhood and adoption (horrifying her family, attorneys and Houston psychiatrists) before giving in to reality.
Rusty Yates contended that as a psychiatrist, Dr. Saeed was responsible for recognizing and properly treating Andrea's psychosis, not a medically untrained person like himself.
Yates claimed that, despite his urging to check her medical records for prior treatment, Dr. Saeed had refused to continue her regimen of the antipsychotic Haldol, the treatment that had worked for her during her first breakdown in 1999.
"The real question to me is: How could she have been so ill and the medical community not diagnose her, not treat her, and obviously not protect our family from her ... Rusty testified that he never knew that she had visions and voices; he said he never knew she had considered killing the children. Neither did Dr. Saeed, even though the delusions could have been found in medical records from 1999 ... he reluctantly prescribed Haldol, the same drug that worked in a drug cocktail for her in 1999. But after a few weeks, he took her off the drug, citing his concerns about side effects ... though her condition seemed to be worsening two days before the drownings, when Rusty drove her to Dr. Saeed's office, he testified, the doctor refused to try Haldol longer or return her to the hospital"
He added that his wife was too sick to be discharged from her last stay in the hospital in May 2001. He said he noticed the staff lower their heads as if in shame and embarrassment, turning away without saying a word. The hospital had no other choice due to the ten-day psychiatric hospitalization insurance constraints of their provider, Blue Cross Blue Shield, subcontracted by Magellan Health Services.
Rusty Yates and his birth family claimed a combination of antidepressants improperly prescribed by Dr. Saeed in the days before the tragedy was responsible for Andrea's violent, psychotic behavior. "Andrea was on 450 mg of Effexor (Venlafaxine hydrochloride), among other medications, and was in his opinion, severely overmedicated ... The psychiatrist said he would reduce the Effexor from 450 mg to 300 mg. He protested and quoted his own extensive research on the antidepressant. He said he read it shouldn't be reduced by more than 75 mg every three or four days, not 150 mg in one day."
According to Dr. Moira Dolan, executive director of the Medical Accountability Network, "homicidal ideation" was added to the warning label of the antidepressant drug Effexor as a rare adverse event, in 2005. Andrea Yates, she said, had been taking 450 mg, twice the recommended maximum dose, for a month before killing her children. Dolan reviewed her medical record at the request of Rusty. "Yates had been prescribed Effexor in varying doses since shortly after her first suicide attempt in 1999, said Dolan, who reviewed her medical records after her first trial at the request of Rusty. A month before the killings, her daily dose had increased to 450 milligrams, twice the recommended maximum dose, Dolan said."
Dr. Lucy Puryear, an expert witness hired by Yates' defense team, countered their contention regarding the administration of her antidepressants, saying the dosages prescribed by Dr. Saeed are not uncommon in practice and had nothing at all to do with her re-emergent psychosis. She suggested rather that her psychosis returned as a result of the Haldol having been discontinued by her doctor two weeks earlier. The oral form of haloperidol (Haldol) takes 4–6 days after discontinuation to reach a terminal plasma level of under 1.5%—a medical standard for "complete" elimination of a drug from the body.
Media outlets alleged that Michael Woroniecki, an itinerant preacher whom Rusty had met while attending Auburn University, bears some responsibility for the deaths due to his "fire and brimstone" message and certain teachings found in his newsletter The Perilous Times that they had received on occasion and which was entered into evidence at the trial.
In the aftermath of her 2006 retrial and insanity verdict, television journalist Chris Cuomo reported on ABC Primetime that: "[Andrea Yates'] delusions were fueled by the extreme religious beliefs of a bizarre, itinerant street preacher named Michael Woroniecki..." Both Rusty Yates and Michael Woroniecki have rejected these accusations.
Rusty Yates said his family's relationship with the Woronieckis was not that close and that Woroniecki did not cause her delusions. Woroniecki maintained that his correspondence with them was with the intention of helping them strengthen their marriage and find the love that he says his own family had found in Jesus. Both men agreed the alleged connection between his message and her mental state was "nothing more than media created fiction".
While in prison, Yates stated she had considered killing the children for two years, adding that they thought she was not a good mother and claimed her sons were developing improperly. She told her jail psychiatrist: "It was the seventh deadly sin. My children weren't righteous. They stumbled because I was evil. The way I was raising them, they could never be saved. They were doomed to perish in the fires of hell." She told her jail psychiatrist that Satan influenced her children and made them more disobedient.
In August 2004 Rusty Yates filed for divorce, stating that he and Andrea had not lived together as a married couple since the day of the killings. The divorce was granted on March 17, 2005, after which Rusty began dating his second wife, Laura Arnold; they married on March 25, 2006. Rusty and his second wife had one son; she filed for divorce in 2015.