A retired aircraft technician has spent the past three months at the Institute of Mental Health (IMH) as a voluntary patient after serving a two-year prison term for killing his wife of 36 years during a psychotic episode.

But Kong Peng Yee, 69, is now facing an appeal that may see him behind bars again.

Although his psychiatric condition is in remission with medication, Mr Kong requires long-term psychiatric follow-up and close monitoring, according to an IMH report.

His two daughters, who were "caught unawares" by the unexpectedly short sentence, were not ready to have him stay with them, the three-judge Court of Appeal said yesterday, during an appeal by prosecutors for a longer sentence.

Mr Kong's sentence - for slashing Madam Wong Chik Yeok, 63, first using a knife and then a chopper, at their Sengkang home on March 13, 2016 - was the shortest ever meted out for intentional culpable homicide here.

Prosecutors had sought nine years' jail but on Oct 16 last year, Mr Kong was given two years' jail by the High Court after he pleaded guilty to a charge of culpable homicide.

As the prison term was backdated to the date of his arrest, he was released from jail on the same day, given the usual one-third remission for good behaviour.

Prosecutors had indicated in the High Court that same day that they would be filing an appeal.

Yesterday, commenting on the family's current arrangement, Judge of Appeal Tay Yong Kwang noted that it was a very difficult situation. "If my dad had done something against my mother, I will still probably be a bit wary," said the judge. This was especially if there were children at home and the triggers for psychosis are not known.

However, he pointed out that there was nothing to stop Mr Kong from leaving IMH if he wanted to.

The court, led by Chief Justice Sundaresh Menon, stressed that the key consideration in determining the sentence in this case was not deterrence but the prevention of any further crime and the protection of the public. The court has asked for further psychiatric evidence before delivering its judgment, which is expected to guide sentencing in future cases involving offenders with mental disorders.

The court wanted to know whether there is a risk of relapse if Mr Kong were to stop taking his medication; whether his prospect of recovery would be enhanced by a stay in a structured environment such as prison to ensure he takes his medication; and whether it is possible to predict how long he has to continue taking medication.

Mr Kong promised the court that he would continue to stay in IMH pending the outcome.

In 2016, he started having delusions that his family was trying to harm him. On March 13, he woke from a nap, took a kitchen knife and stabbed Madam Wong until she was dead. He then told his sister to call the police and also wrote on a piece of paper how his assets should be distributed.

An autopsy noted 189 injuries.