Kevin Reddington, the lawyer who defended Lindsay Clancy, won the admiration of many women around the country who became engrossed in the trial and saw him as calling out a health care system that they believe failed her. But if the social media embrace of Mr. Reddington is new, his interest in mental health defenses, and the concerns of female defendants, are not. His long career has touched on similar themes before, including in a milestone Massachusetts case more than 30 years ago, when he became the first lawyer to win an acquittal by arguing that battered women's syndrome could cause temporary insanity. Mr. Reddington, 75, also defended Catherine Greig, the longtime girlfriend of the notorious Boston gangster James (Whitey) Bulger, when she was charged with harboring a fugitive. Mr. Bulger's lawyer, J.W. Carney Jr., is a friend of Mr. Reddington's who has popped into court to watch him work Ms. Clancy's case.

Mr. Reddington, who is based in Brockton, Mass., a working-class city, was brought on to represent Ms. Clancy almost immediately after she killed her children in 2023 by strangling them with exercise bands. In court, he described visiting the crime scene with her former husband, Patrick Clancy, when blood from her suicide attempt just after the killings still stained the bedroom floor. He recalled gazing down at her in her hospital bed soon after her surgery for her spinal injury and wondering, "What kind of demons, what kind of horror, was in her mind?"

His courtroom demeanor often suggested that of an aggrieved grandfather, as he clutched Ms. Clancy's hand in moments of emotional distress and referred to her repeatedly as "this young lady." At the start of his closing argument last week, Mr. Reddington's voice was quiet as he spoke the names of the three Clancy children: Cora, Dawson, Callan. He grew louder as he turned his focus to Ms. Clancy. "This is a prosecution," he said, "that has ripped the soul out of this girl."