A Duxbury man who killed his father by repeatedly dunking his head underwater while performing what he described to authorities as a baptism and exorcism was convicted Thursday of involuntary manslaughter, court records show.
Jack H. Callahan had been charged with first-degree murder and his lawyer, Kevin J. Reddington, argued at trial that his client was not responsible for the death of his father, Scott Callahan, 57, in June 2021.
At the time of his arrest, Jack Callahan told police he had brought his father to Island Creek Pond in Duxbury after retrieving him from a Boston bar, not long after he had walked away from a treatment center for chronic alcohol abuse, prosecutors said.
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Jack Callahan, who was then 19, told authorities he was exorcising a demon within his father named “Dirty Dan” and had given his father a choice while they were in the pond — to go to heaven or hell.
“I believe he chose hell,” Callahan told police.
At his arraignment in 2021, Plymouth Assistant District Attorney Shanan Buckingham said Callahan “believed he was baptizing his father.”
“He was holding his father in the pond on his back like a baby and he continually dunked his head under the water about four to eight times,” she said. “When his father started to cough and choke, he would lift his head up. And when the father started fighting, he would strike him and push his head back down into the water.”
Sentencing is scheduled for May 3 in Brockton Superior Court. The involuntary manslaughter conviction carries a sentence of up to a maximum of 20 years imprisonment.
John R. Ellement can be reached at john.ellement@globe.com. Follow him @JREbosglobe.