Neama Rahmani, a former federal prosecutor, told PEOPLE he expects prosecutors to retry the case.
"She will be prosecuted," Rahmani said Friday.
Before the mistrial was declared, Rahmani had predicted there was "almost 100%" certainty prosecutors would pursue a retrial if the jury failed to reach a verdict. He pointed to the deaths of Clancy's three children and the public pressure prosecutors could face if they decided not to continue the case.
"There are three dead children," Rahmani said, arguing that political pressure on prosecutors would likely be significant. He added that failing to prosecute could result in Clancy being released rather than placed in a psychiatric facility.
Despite expecting a retrial, Rahmani believes a conviction could be difficult to secure. He said it appeared that 11 jurors were inclined toward a not-guilty verdict, while one juror disagreed.
Clancy's attorney, Kevin Reddington, previously said he also expected prosecutors to retry the case, although he suggested they could consider lesser charges rather than first-degree murder.
Judge William Sullivan declared the mistrial after jurors sent a third note indicating they could not reach a unanimous decision. The jury had deliberated for nearly a week and had been considering first-degree murder, second-degree murder and manslaughter charges.
Clancy pleaded not guilty by lack of criminal responsibility. Her defense argued that she was experiencing psychosis and had been overmedicated when she killed her three children, Cora, 5, Dawson, 3, and Callan, 8 months old.
The children were fatally strangled with exercise bands at their family home in Duxbury, Massachusetts, in January 2023. Afterward, Clancy jumped from a second-story window in what prosecutors described as an apparent suicide attempt.
Prosecutors maintained that Clancy intentionally killed her children and was not experiencing psychosis at the time. Assistant District Attorney Jennifer Sprague argued that Clancy was depressed and suicidal but viewed her children as a protective factor.
Reddington argued during closing statements that Clancy had sought help for postpartum mental health problems but was failed by medical providers.
The weeks-long trial included testimony from dozens of witnesses, including police officers, medical professionals, expert witnesses and Clancy's former husband, Patrick Clancy.
With the jury unable to reach a verdict, the prosecution must now decide whether to bring the case before another jury.
