A 27-year-old Thurles man believed he was on a mission for the IRA when he killed his parents in September 1998. Martin Doherty told a jury in the Central Criminal Court today that in the lead up to what he called the crime, the murders, he was experiencing an intense period of paranoia, of receiving messages in his head. He interpreted a wide range of day to day gestures and actions as having significant meanings for him. Mr Doherty is claiming he was insane at the time of the killings and suffers from schizophrenia.

"The world became a battlefield for me," Martin Doherty said in the witness box today as he recalled his state of mind in the weeks leading up to his parents deaths in September 1998. He killed William and Teresa Doherty in their Thurles home. He believed the IRA was telling him to kill his father to avenge the murder of his uncle, Paddy, in London in the 60s. He was striking a blow for good people, he believed.

He believed that his Uncle had been murdered by MI5 while he was on a bombing mission for the IRA and that his father had informed on him. His uncle was killed in unrelated circumstances and, in the witness box today, Martin Doherty accepted that there was no truth in the rest of the fantasy that had seemed so real to him at that time. He also said today that his belief that his father had sexually abused him was untrue, but, for a time, nothing would convince him that it did not happen. He even believed he was passed around as a sex toy among his father's Garda colleagues.

He told his lawyer Paddy McEntee about his life as a teenager and young man - slashing his wrists, believing he was a paedophile, that his arms and legs were expanding and that everyone was talking about him. In the weeks immediately before his parents' deaths, he interpreted every gesture by people as signals to him: "People touching their noses, folding their arms or legs, coughing... it was endless," he said. He was also told to kill his mother. He resisted until a convincing message he believed he had received from a pack of tobacco.

"It's crazy," he said. "But it's what I experienced." Mr McEntee told the jury today that the psychiatric evidence, which is accepted by doctors at the Central Mentral Hospital, is that Martin Doherty suffers from schizophrenia and was in a psychotic state when he killed his parents. He will continue his evidence tomorrow.