More than three years after a Massachusetts mother strangled her three young children, her former husband described returning home to the aftermath and a jury listened on Wednesday to his frantic 911 call, as her lawyers seek to prove she was in the grip of post-pregnancy psychosis.

Lindsay Clancy, 35, admits she killed her children in January 2023 while her then husband was on an errand away from their home in the Boston suburb of Duxbury. Her attorney says she was driven by postpartum mental illness and a jury cannot find she intentionally murdered the children.

Patrick Clancy, now divorced from Lindsay Clancy, recounted during his first day on the stand on Monday how she had told him in the months prior that she was having thoughts of suicide and harming their children. He said she was prescribed medications and had stayed at a psychiatric hospital earlier that month.

But he said she showed no signs she planned to hurt herself or her kids after she was discharged, and had a “normal” demeanor when he left to fetch takeout food and pick up stool softener for one of their children at a pharmacy.

Patrick Clancy’s last fleeting image of three-year-old Dawson was his son on the couch eating chicken nuggets and green beans. Lindsay Clancy had asked her then husband to pick up food and stop by the pharmacy. Prosecutors say this shows she acted intentionally and bears full responsibility for the deaths of Dawson, five-year-old Cora and eight-month-old Callan.

Jurors watched surveillance video from the pharmacy showing Patrick Clancy call his wife with a question about which medicine to get.

“She was pretty quiet. It sounded like she was busy,” he testified on Wednesday. “I remember hanging up thinking she was probably in the middle of giving baths or something like that.”

When he came home, the house was silent.

He searched until finding a lot of blood in the main bedroom. Lindsay Clancy had used multiple methods to try to end her own life. She remains paralyzed from the waist down after jumping from the home’s second-story window.

Badly injured but conscious, she told her husband that the kids were in the basement, without saying they were dead, he testified.

Jurors listened to the 911 call as he discovers the children, who were strangled with exercise bands. Patrick Clancy sobs and screams, “oh my God!”. A confused dispatcher keeps asking what happened, before he says: “She killed the kids.”

In the courtroom, Lindsay Clancy sobbed as the 911 call was played, and her parents also appeared to be crying. Patrick Clancy had left the court after finishing his testimony.

Whether she killed her children is not in dispute. But her attorney argues that she was driven by postpartum psychosis, a rare mental illness linked to the stress, sleep deprivation and hormonal changes that follow childbirth. Her lawyer said she had bipolar disorder, and that antidepressants prescribed after the birth of her third child worsened her condition.

On the day of the killings, Lindsay Clancy said she heard voices telling her, “This is your last chance. Kill the children so you can kill yourself,” according to her lawyer.

If convicted of murder, she faces life in prison without parole. If found not guilty due to a lack of criminal responsibility, she would be committed to a state mental health facility.

Lindsay Clancy had sought care from experts in post-pregnancy mood disorders, was put on multiple psychiatric medications, and when nothing worked, checked in to a psychiatric hospital. She killed the children 19 days after she was discharged.

Patrick Clancy testified on Monday about her deteriorating mental health in the months before the killings, including describing intrusive thoughts of harming the children and of suicide. But he said she appeared to be doing better as recently as two weeks before the killings on 24 January 2023.

He testified on Monday that the day of the killings started as one of her “best days”. She took Cora to a doctor’s appointment and then returned home to build a snowman with the children and work on art projects.

Postpartum psychosis, different from postpartum depression, is rare and estimated to afflict only one to two per 1,000 women after delivery. Experts at the Cleveland Clinic describe it as a mental health emergency affecting someone’s sense of reality.