SINGAPORE - A 46-year-old man of unsound mind was ordered to be confined at the President's pleasure on Tuesday (Nov 3) after the High Court found, following a trial, that he had killed his 75-year-old father.

Justice Valerie Thean concluded that Tan Kok Meng, who was left alone for three hours with his father at their Bedok North flat, had caused the death of the older man on Nov 13, 2015.

When Tan's mother returned to the flat to find her husband, Mr Tan Ah Hin, covered in blood, the gate was still padlocked and there was no sign of forced entry.

"No one else could have been responsible for (Mr Tan Ah Hin's) injuries, which were not accidental," said the judge.

Although Tan was found to have committed the act of killing, under the law, he was acquitted of murder due to his mental incapacity.

Two psychiatrists from the Institute of Mental Health had diagnosed him with schizophrenia and found that he was of unsound mind during the killing.

Tan will be confined in a psychiatric institution, prison or some other place of safe custody.

There is no minimum period of detention and the mental state of the detainee is reviewed regularly until he is suitable for discharge.

"This is grief twice over for the family and I would emphasise that this order is made in the context that Kok Meng has been acquitted of the offence charged," said the judge.

"The object the law seeks to fulfil by this order is the protection of society, and by the same means, the safety of the accused and his family. It is hoped these reasons bring some measure of closure to what I am sure is a painful chapter for the family."

After the verdict, Tan appeared to be in good spirits and was allowed by the court to speak to a few family members.

He was accused of inflicting multiple blows on the victim's face and strangling him.

During the trial, the court heard that his family members described Tan as "unstable" on the day of the offence.

His mother, Madam Toh Meow Siang, noted that he had been looking dazed for the previous two days and had been pacing up and down in the flat.

Before Madam Toh left the flat at about 2.30pm, she told her husband not to allow their son to go out.

About three hours later, she returned to find her husband breathing heavily, lying in a pool of blood under his head. Tan, who was seated on the sofa, did not respond to her questions.

Madam Toh left the flat to get help from the neighbours and when she returned, she shouted at Tan, asking why he had killed his father.

Tan then walked over to the older man, sat on his abdomen and placed his hands on his father's upper chest before she pulled him away.

The paramedics arrived soon after.

As they attended to the victim, Tan, who was covered in dried blood, suddenly got up from the sofa where he had been sitting in a daze.

Ignoring the pleas of the paramedics, he choked his father while mumbling "I want him to die" in Mandarin for a minute or so, then went back to sit on the sofa.

A paramedic said she shouted at Tan to stop but he ignored her.

Police officers arrived shortly after and arrested Tan.

He told them that he used his bare hands to attack his father, that they had a strained relationship and that the older man had called him "good for nothing".

The victim stopped breathing in the ambulance and was pronounced dead at Changi General Hospital.

An autopsy found the older Tan died from strangulation and blood aspiration.

Tan was defended by Mr Favian Kang and Mr Nichol Yeo.