An alcoholic father was drowned in an attempted 'exorcism' after his son decided to confront the 'demon' he saw in his father's eyes, a Massachusetts court has heard.

Jack Callahan, 22, has gone on trial at at Plymouth County Superior Court for the murder of his father Scott, 57, who was found by police floating in a pond outside Duxbury, around 30 miles outside of Boston, in June 2021.

The then 19-year-old told police his banker father was possessed by a demon called 'Dirty Dan' who he thought could be destroyed through baptism.

Callahan was bringing his father home from a Boston bar when his mother, Wendy, called to say she would not have her ex-husband in their house, and the young man asked their cab driver to pull over next to the pond.

He grabbed his father and repeatedly plunged his head under the water, telling cops: 'I left him there to decide, you can come to heaven with me or hell. I think he chose hell.'

Jack Callahan, 22, is pictured on his father Scott's left alongside his mother Wendy and his two brothers Will and Charlie in 2016. The parents were divorced when Jack allegedly murdered his father in June 2021

Jack Callahan, 22, has gone on trial for the murder of his father Scott during an 'exorcism'

Police found Scott Callahan (pictured with a unnamed woman) dead in a pond outside Duxbury, Massachusetts in July 2021  

Scott Callahan (pictured in an undated photo from his obituary page) was a heavy drinker. His son had gone to collect him from a bar on the night of the alleged killing 

Jack Callahan told police he had been bringing his father home from a bar when they stopped next to Island Creek Pond where his father began attacking him

Scott Callahan's obituary reported that he was the Senior Vice President of Texas Capital Bank, and had an 'extensive career in finance'.

He had been receiving treatment for alcoholism at a center in Hopkinton before he checked himself out and headed for the bar in Boston.

The teenager called an Uber to bring him back to the $1.5 million home in Duxbury and said his father began to attack him when he asked the driver to pull over at around midnight.

'He indicated that the victim had been punching him in the face,' Plymouth Assistant District Attorney Shanan Buckingham said at Callahan's 2021 arraignment.

'He went on to state that in this incident at the pond, he believed he was baptizing his father.

'He described that he was holding his father in the pond on his back like a baby, that he continually dunked the father's head in the water about four to eight times, that when the father started to cough and choke, he would lift his head up.

'And then when the father started to fight and strike him, he would push the head back into the water. 

'He did so until his father was no longer struggling and floating.'

Jack Callahan, 21, cried when he first pleaded not guilty at Plymouth District Court in 2021

According to Buckingham, Callahan held his father in the pond on his back like a baby, and continually dunked his head in the water about four-to-eight times 

Authorities said Callahan went to a bar in Boston Sunday night to pick up his father, Scott Callahan, 57, who was not supposed to be drinking 

Scott Callahan's obituary reported that he was the Senior Vice President of Texas Capital Bank, and had an 'extensive career in finance'

The family lived in this $1.5 million five-bedroom house outside Duxbury 

Wendy Callahan with her children Jack, Will and Charlie a year before Scott's death

Wendy Callahan with sons Jack and Will at a birthday dinner in 2019 

Scott Callahan had been receiving treatment for alcoholism at a center in Hopkinton before he checked himself out and headed for a Boston bar on his last night 

Officers attempted CPR on the Colorado State University graduate before he was taken to Plymouth's Beth Israel Deaconess Hospital where he was pronounced dead

The teen's mother saw him finally arrive home in soaking wet clothes at about 2am when she called police to tell them he was having a mental health episode and her ex-husband was missing.

'The mother indicated that the defendant had not exhibited this behavior before and that he had no history of mental illness,' Buckingham said.

Police called an ambulance after finding Callahan 'worked up and distraught', hyperventilating and passing out.

He told them his father hit him, and he did not know where he was: 'He's missing. I don't know what happened. I blacked out.'

He eventually directed the police to Crooker Memorial Park where officers found Scott in Island Creek Pond.

Officers attempted CPR on the Colorado State University graduate before he was taken to Plymouth's Beth Israel Deaconess Hospital where he was pronounced dead.

The teen was arrested the following day and cried in court as he pleaded not guilty at the first hearing in 2021.

Callahan's attorney Kevin Reddington asked the judge to send the teen to Bridgewater State Hospital for a mental health evaluation, warning that he was a danger to himself.

'He's a very nice young man,' Reddington said, 'He comes from a wonderful family.

Scott Callahan in an undated photo. He was the Senior Vice President of Texas Capital Bank, and had an 'extensive career in finance'

Plymouth Superior Court Judge William Sullivan is hearing the case which is expected to take ten days 

The public gallery was packed as the trial got underway on Friday

Jack Callahan, 22, at Plymouth Superior Court in Brockton on Wednesday April 17, 2024

'My client had a concern for his father, knowing that he would be drinking and knowing that he shouldn't be.

'He was going to try to take him back where he should be.'

His mother told the court that he had been living with a brother in Colorado and had to leave his job in the logging industry after injuring his back before returning to Duxbury to live with his mother.

Callahan has pleaded not guilty to murder and the trial is expected to last for 10 days.