While taking more than a dozen medications — including Ambien, Klonopin, Valium, Prozac, Ativan, Zoloft and Seroquel — over several months, Ms. Clancy experienced worsening insomnia, anxiety and depression. By December 2022, she was reporting panic, numbness, racing thoughts, suicidal ideation and a growing fear “that something awful might happen,” according to the lawsuit.

Late that month, she admitted herself to a day program for patients with postpartum depression. On Jan. 1, 2023, after the day program determined that she needed a different level of care, she admitted herself to McLean Hospital, a residential psychiatric campus outside Boston, where she stayed for five days.

According to the lawsuit and medical records, Ms. Clancy’s crisis came to a head on Jan. 24, 2023, when she heard “a compelling and unrecognizable singular male voice” telling her that “she should die, that this is her last chance, and that her children would suffer if she was gone.” That day, after ordering takeout food for dinner just after 5 p.m. and asking her husband to pick it up, prosecutors say, she killed Cora and Dawson and fatally injured Callan, who died three days later.

Ms. Clancy then cut her wrists and neck, jumped from a second-story window, and fell about 20 feet to the ground, where her husband found her when he returned home less than 30 minutes later. She suffered traumatic spinal cord injuries and remains unable to walk, according to her lawyer.

Prosectors say she acted with “deliberate, premeditated and extreme atrocity and cruelty.” Ms. Clancy consulted a mapping app before her husband left the house to determine how long he would be gone, they said in documents, and “gave herself the time and privacy needed to commit these murders.”