A murder suspect who allegedly joined forces with a friend to kill his father and make an attempt on his mother's life was suffering from a short-term mental illness that triggered delusions which affected his behaviour, a private psychiatrist testified yesterday.
Defence witness Dr Yu Wai-tak said he had diagnosed Ian Lee Christoffer Fok Lap-yin, 20, as having a brief psychotic disorder, which would last less than six months.
Yu said he believed Fok was under the influence of his delusions from about two weeks before the attack on his parents.
Government psychiatrist Dr Kavin Chow Kit-wan disagreed with the diagnosis. She found Fok did not suffer from psychosis and was not affected by delusions, the Court of First Instance heard.
Ian Fok denies murdering his father, Fok Lai-chi, 50, and attempting to murder his mother, Irene Fok, 40, at their home in Pat Heung, Yuen Long, on March 16 last year. His former schoolmate, Chan Ming-tin, 20, has pleaded guilty to murder.
At yesterday's hearing, Yu said that in May this year, he met Ian Fok for more than two hours. He found his patient "full of fantasies" that affected his mind.
"His fantasies later became delusions, and he lost his ability to [differentiate between] delusion and fantasy in the real world," Yu said.
Fok claimed he had fantasised about becoming a leader in another world and had to kill his parents to save the world, Yu said. "He had absolute conviction of his wrong beliefs at that time."
The symptoms of brief psychotic disorder included delusions, hallucinations, disorganised speech or behaviour, or catatonic behaviour, Yu said. Fok had only delusions, and he had since recovered, the court heard.
Prosecutor Diane Crebbin asked Yu how Fok - if his delusion was so severe two weeks before the incident - could have made such a detailed plan of attack.
She suggested Fok was "cold-bloodedly doing what had happened" and lacked remorse afterwards.
The doctor admitted he had failed to notice any remorse from Fok over his father's death, but said the disorder might not affect the patient's organising ability.
Yu cited John Hinckley Jnr, who tried to kill US president Ronald Reagan in March 1981. Hinckley, who had a similar illness, managed to buy a gun, look for the president and carry out the assassination, he said.
The court also heard from Chow, who refuted Fok's repeated claims that he had multiple personality disorder.
Since March last year, Chow had met Fok 14 times at the Siu Lam Psychiatric Centre.
He had told her voluntarily about his 16 identities, which she believed stemmed from his fantasies as he knew they were fake.
"People who suffer from multiple personality disorder usually have no memory of their identities and do not know of the co-existence of the other identities."
Chow said delusion was a false belief that a person thought was true, but this was not so with Fok. She talked to his teachers but they could not support his story about the multiple identities.
Fok once told her he had collapsed while in custody, she said, but she could not find such a record in the nursing report.