A man accused of murdering Det Garda Colm Horkan has told a court he had been diagnosed with two mental disorders, had stopped taking his medication and was living in a shed without running water in the weeks before the shooting that killed the detective.

Stephen Silver took the stand Wednesday after the indictment was closed. He told his barrister, Róisín Lacey SC, that he had considered signing up for respite the day before the shooting, but on the day of the shooting he felt “hyper” and “elated” and “it went too far”. He said he began “thinking strange things”, such as that the Australian woman he was seeing was an MI6 agent and that the SAS had planted a bomb under his van.

Earlier in the day, the court heard CCTV footage of him looking under his van in a “crouching” position in a car park outside a Dublin hotel. He also said he believed he was a member of the Irish Army’s 62nd Cavalry Reserve and that when he put on his Roscommon hat and leather vest, he was wearing an Irish Army uniform and was going to “police the streets for Covid”.

Mr Silver (46), a motorcycle mechanic from Ogward, Foxford, Co Mayo, pleaded not guilty to murdering Det Garda Horkan knowing or being reckless as to whether he was a member of An Garda Síochána, acting under their duties. He pleaded guilty to manslaughter by reason of limitation of liability in Castlereagh, County Roscommon, on 17 June 2020.

Mr Silver told Ms Lacy he grew up in Roscommon and trained as a car mechanic after leaving school following his Junior Certificate exams. He said he had a “long psychiatric history”, having been admitted to psychiatric wards 17 times since he was 19 or 20 years old. Some of the confessions were voluntary, others involuntary, he said, and he has been diagnosed with schizoaffective disorder and bipolar disorder.

Jurors heard that on one occasion in 2003, the Gorkan Police Department committed Mr. Silver to a psychiatric unit. Defendant said he remembered the incident, but not the Horkan Department. He added: “I was very upset at the time, so I didn’t remember much.”

He was married for about 13 years but separated from his wife in February 2020. “We weren’t doing well at the time,” he said. He moved into a flat in Foxford but couldn’t afford the rent so he moved out and moved into a shed he bought to expand his motorcycle mechanics business.

He was prescribed olanzapine to treat mental disorders, but was off the medication.

On the day Det Garda Horkan was shot, Mr Silver recalled becoming very talkative. He said he was getting “hyper”, “talking gibberish”.

On his return to Castlereagh from Dublin that day, he learned that an armed guard had broken into the house of his old friend James Coyne, and went to see him. They hadn’t seen each other in about 13 years, he said, but they hugged and shook hands.

They decided to go to Mr Silver’s bike repair shop in Foxford but stopped at Castlerea Garda Station on the way. Mr Silver said he did not remember what he said to the guards, but had intended to “tell them not to treat James badly”. He remembered how he “had a conversation” with the guard sitting at the table.

Mr Silver will continue his evidence before Judge Paul McDermott and a jury of seven men and five women on Thursday.