SINGAPORE - A bus driver who held delusions that his wife of 28 years was cheating on him and stabbed her to death in their Loyang condominium in 2017 pleaded guilty in the High Court on Tuesday (July 28) to a reduced charge of culpable homicide.

The prosecution is seeking 12 years' jail for Krishnan Raju, 53, while the defence is asking for eight years.

Krishnan was originally charged with murder for repeatedly stabbing Madam Raithena Vaithena Samy, 44, an operations executive, on the night of Oct 26, 2017, at their Loyang Gardens home.

She suffered 13 stab wounds, including five to the chest which were fatal.

The charge was reduced after he was diagnosed by an Institute of Mental Health (IMH) psychiatrist with a type of delusional disorder in which the sufferer is preoccupied with the thought that his spouse is unfaithful, without any real proof.

Dr Cheow Enquan found that Krishnan's disorder, which is also known as morbid jealousy, had substantially impaired his mental responsibility for the killing.

The court heard that Krishnan had been very possessive of Madam Raithena. Family members, including their two children, aged 22 and 20, noticed that he kept tabs on her whereabouts.

The couple's relationship started breaking down in December 2016.

Krishnan felt that her attitude towards him had changed. He claimed that she often come home late in a drunken state and made excuses not to have sex with him.

He began stalking her, and once showed up at her hotel when she went to Malacca for a company event.

He checked her phone and underwear and also made allegations of her infidelity in front of other family members, which led her to ask for a divorce.

Following an argument in October 2017, when he threatened suicide, Madam Raithena moved out of the master bedroom to sleep in her daughter's room.

He then planted an audio recording device in that room to listen to his wife's conversations.

On the night of Oct 26, 2017, Krishnan started drinking as he listened to a recording in which he heard his wife laugh and mention a man's name, "Saravanan".

He believed that she was laughing at him and suspected that she was having an affair with Saravanan.

That night, Madam Raithena returned home at about 9pm. By this time, Krishnan had downed a 200ml bottle of gin.

When she went to take a shower, he entered the bathroom and stabbed her with a kitchen knife.

Krishnan then dragged her out to listen to the audio clip but she struggled and begged him to stop.

He then stabbed her repeatedly and grabbed her neck until she stopped moving.

Krishnan left the flat as Madam Raithena gasped for breath. At around 10.10pm, he sent a text message to his family members: "Forgave (sic) me".

Krishnan fled to Johor Baru and stayed at his elder brother's place that night.

His daughter and nephew found Madam Raithena's body at about midnight.

Krishnan returned to Singapore at about 10.45am the next day and surrendered himself.

Police investigations revealed that Madam Raithena had been having an affair with a male colleague since November 2016, but none of her family members or friends knew about it.

This, however, did not affect the diagnosis.

Dr Cheow noted that despite Krishnan not having any concrete evidence, the intensity and degree of his belief that she was having an affair were evident from his actions.

Krishnan was so preoccupied with his wife's unfaithfulness that he could not cope with his job and started drinking heavily in the weeks leading up to the killing, noted the psychiatrist.

Dr Cheow also found that Krishnan was in a state of "acute alcohol intoxication" when he killed his wife - a point disputed by defence psychiatrist Rajesh Jacob.

The case continues with a hearing for the court to decide on this point, which has a bearing on the sentence.