PLYMOUTH, MASS. (WHDH) - A 19-year-old man accused of murdering his father in a pond in Duxbury early Monday morning told investigators that he was baptizing his dad in the water because he believed he was possessed by a demon and needed to exorcise the evil spirits, a prosecutor said.

Jack Callahan, a 2020 graduate of Norwell High School, was arraigned Tuesday in Plymouth District Court on a charge of murder in connection with the death of his 57-year-old father, Scott Callahan, according to the Plymouth District Attorney’s Office. A not guilty plea was entered on his behalf.

Police received a call around 2 a.m. on Monday from Jack’s mother who said her son had arrived home in wet clothes and told her that his father was missing, authorities said. Officers who responded to the home said Jack was in a mental state and hyperventilating.

Investigators later determined that the father and son were riding in a Uber from a Boston bar to their Duxbury home when they were dropped off at Crocker Park in the area of Island Creek Pond, prosecutor Shanan Buckingham told the court.

“The defendant in the Uber used the Uber driver’s phone to make a phone call to his mother, where his mother was overheard saying that he could not bring the victim to their house,” Buckingham explained. “It was believed at the time from witnesses that the victim appeared to be intoxicated…The defendant then ordered the Uber driver to go to the pond.”

Buckingham noted that the victim suffered from substance abuse issues and a brain injury that made his “executive functions questionable.” Jack’s mother and father were also said to be divorced.

Officers who responded to the park discovered items belonging to the son before finding the father in the water floating near two pieces of luggage, police said.

The victim was pulled out of the water and emergency crews began CPR. He was then transported to Beth Israel Deaconess Hospital in Plymouth, where police say he was pronounced dead.

When initially asked about the whereabouts of his father, Jack allegedly told investigators, “He’s missing. I don’t know what happened. I blacked out.”

During an interview with officers at the hospital on Monday, Jack allegedly stated that he used the Uber to go to the bar to pick up his dad, who had left a treatment center in Hopkinton where he was being treated for alcohol abuse. In an altercation that ensued at the pond, Jack reportedly saw a “demon” in his father’s eyes.

“He went on to state — in this incident at the pond — that he believed he was baptizing his father. He described that he was holding his father in the pond, on his back, like a baby,” Buckingham said. “He continually dunked the father’s head in the water, about four to eight times…When the father started to fight and strike him, he pushed the head back down into the water. He did so until his father was no longer struggling.”

Jack also told investigators that he was trying to exorcise his father’s demonic spirits, one of which he referred to as “Dirty Dan,” Buckingham added.

Witnesses told investigators that Jack may have been suffering from ongoing mental health issues that had “recently surfaced,” according to Buckingham.

Defense attorney Kevin Reddington  called his client a “very nice young man” and said that he plans to hire a private investigator to take a closer look at the facts surrounding the case.

District Attorney Tim Cruz noted that his office is awaiting the victim’s autopsy results.

At Buckingham’s request, a judge ordered Jack held without bail. He is due back in court on Aug. 12.

An investigation remains ongoing.

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