A 69-year-old retired aircraft technician, who developed delusional beliefs that his family was trying to harm him, decided to make a pre-emptive strike by killing his wife of 36 years, the High Court heard yesterday.

Kong Peng Yee pleaded guilty to a charge of culpable homicide by slashing Madam Wong Chik Yeok's head, first using a knife and then a chopper, at their Sengkang home on March 13 last year.

He told police that his mind told him to "make sure she die" and that he was "happy" on realising that she was dead.

He was initially charged with murder but the charge was reduced, as a psychiatric assessment by Dr Kenneth Koh from the Institute of Mental Health found that his mental responsibility for his actions had been substantially impaired by his psychotic delusions.

Kong's psychotic state could have its origins in severe depression following mild physical impairments after his eye surgery, said Dr Koh's report in April last year.

A further report in May this year said Kong had a "brief psychotic episode" at the time. Kong, who was treated for his psychiatric disorder in prison, no longer suffers from the delusions.

The court heard that Kong and Madam Wong, 63, lived with their younger daughter Yanni, 27, in Compassvale Crescent. Their older daughter Annie, 36, lived elsewhere.

In January last year, Kong underwent cataract surgery. Over time, he began to associate other ailments, such as constipation, weakened knees and insomnia, with his surgery or his food intake.

On March 12, Kong and his wife spent the night at Annie's place. He told her to take care of her younger sister if he was not around. He also told Annie that he did not think she was his biological daughter.

The next day, Kong started behaving in an abnormal manner while at church with his wife and Annie.

After church, Annie drove her parents home and left to meet Yanni.

Kong, who had taken a nap, claimed that he woke up to roaring sounds. He took a knife from the kitchen sink and stabbed Madam Wong in the back while she was folding clothes in the living room.

He moved to her front and continued stabbing her.

When the knife dropped to the floor, he went to the kitchen to get a chopper and continued attacking his wife, stopping only when he realised that she was dead.

He phoned Yanni, but she missed his call.

He then called his younger sister and told her that he had killed his wife. He told her to call the police and to distribute his money to his daughters.

When Yanni returned his call, he told her: "I killed mummy." When she told him not to talk nonsense, he replied: "Already killed."

When his daughters arrived at the flat with police officers, Kong was sitting on the sofa in blood- stained clothes, and Madam Wong was motionless on the bloodied floor.

An autopsy noted 189 injuries, including knife wounds and bruises, mostly around her head and neck. She bled to death from multiple slash wounds to the head.

Kong told police that he believed his family would not look after him if he was unwell, that Annie had reconciled with her "real" parents, and that he should kill his wife first because his family might want to kill him.

The case was adjourned for sentencing after Justice Choo Han Teck said he would like to ask Dr Koh some questions.

Deputy Public Prosecutor Sarah Shi sought at least nine years in jail, while defence counsel Sunil Sudheesan asked for five years in jail.