Callan Clancy passed away just after 11 a.m. on Friday, Jan. 27, WPRI reports citing Plymouth County District Attorney Tim Cruz.
The baby boy was discovered along with his older siblings Cora and Dawson Clancy "with obvious signs of trauma" at a home at 47 Summer Street in Duxbury on Tuesday, authorities said.
Cora, age 5, and Dawson, age 3, were taken to a local hospital where they were pronounced dead later that night.
The children's mother, Lindsay Clancy, has already been charged with the deaths of Cora and Dawson but authorities have yet to announce any new charges for Cullen's death. She then tried committing suicide by jumping out of a second-story window, according to authorities.
It has since been speculated that Lindsay was battling postpartum psychosis and that the mental illness drove her to allegedly strangle her children to death.
Lindsay was treated on scene before being taken to a local hospital for treatment where she remains and placed into police custody.
She was charged with two counts of homicide and three counts each of strangulation, and assault and battery with a deadly weapon on Wednesday.
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