A Massachusetts man has been convicted of involuntary manslaughter in the death of his father, which happened during a baptism-style exorcism at a Duxbury pond, according to prosecutors.Jack Callahan, 22, of Duxbury, was found guilty by a jury in Plymouth Superior Court after an eight-day trial and approximately 25 hours of deliberations, Plymouth County District Attorney Tim Cruz announced Thursday.Callahan was 19 years old when he was initially charged with murder in connection with 2021 the death of his 57-year-old father, Scott Callahan.Prosecutors said that at about 2 a.m. on June 28, 2021, Duxbury police received a call from Jack Callahan's mother, who said that her son was acting erratically after he arrived at her Sampson Street home and that he said his father was missing in the area of Island Creek Pond at Crocker Memorial Park.Duxbury police responded to the home and found Jack Callahan distraught and hyperventilating, authorities said. At about the same time, prosecutors said Duxbury police officers and firefighters responded to Island Creek Pond.The first responders who went to Island Creek Pond found Scott Callahan submerged in the water, approximately 50 feet away from the shore, prosecutors said. Emergency medical services personnel began performing CPR on Callahan and transported him to Beth Israel Deaconess Medical Center-Plymouth, where he was pronounced dead.When Jack Callahan was arraigned on a murder charge shortly after his father's death, prosecutors said he told police that he went to Boston to get his father, who was at a bar. Both the prosecution and defense acknowledged that Scott Callahan had a long history of substance abuse and suffered from the aftermath of a traumatic brain injury.Jack Callahan told police that his mother did not want her intoxicated ex-husband at the family home that night, so an Uber dropped the pair off at Island Creek Pond around midnight, prosecutors said.Prosecutors said Jack Callahan told police his father hit him several times at the pond, and that is when he decided to "baptize" his father.“(Jack Callahan) believed he was baptizing his father. He described holding him on his back like a baby, that he continually dunked the father’s head in the water four to eight times,” Assistant District Attorney Shanan Buckingham said in June 2021. “He did so until his father was no longer struggling and floating.”Cruz said the state's Office of the Chief Medical Examiner found the cause of Scott Callahan's death was drowning and ruled the manner of his death was homicide. The OCME reported that Callahan had water-logged lungs and an abrasion on his head, according to the district attorney.Duxbury police said they arrested Jack Callahan at about 10:35 a.m. on June 21, 2021, at BIDMC-Plymouth, where he underwent a psychiatric evaluation.During Jack Callahan's arraignment, his defense attorney requested a psychological valuation at Bridgewater State Hospital, but the judge denied the request. Callahan was instead ordered held without bail pending a dangerousness hearing.Cruz said Jack Callahan is scheduled to be sentenced next Friday, May 3.