SINGAPORE - Reacting to being hit with a tray and being scolded, socialite Nancy Gan Wan Geok's domestic helper swung her employer's head against a wall, causing multiple skull fractures, then drowned her in the pool of her own house.

Indonesian Dewi Sukowati, 20, pleaded guilty and was sentenced to 18 years' jail on Tuesday (May 31) for culpable homicide not amounting to murder of the 69-year-old Madam Gan.

The court heard that on March 19, 2014, at about 7.30am, Dewi - then 18 - had taken a glass of water on a tray to Madam Gan in her home at Victoria Park Road in Bukit Timah.

It was her sixth day of work with Madam Gan. According to the statement of facts of the case, Madam Gan was upset that the glass was on the wrong type of tray. She splashed the water on Dewi's face and threw the tray on the floor.

When Dewi bent down to pick up the tray, Madam Gan snatched it from her and hit her on the back of her head with it, while she was still squatting down.

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She also scolded the teenager and threatened to reduce her salary to $200, said the statement of facts.

Dewi lost control of herself, grabbed Madam Gan by the hair and swung her head into the wall with all her strength.The back of Madam Gan's head hit the wall and started bleeding profusely. She collapsed unconscious.

Dewi was frightened and stayed where she was, thinking about what she had done.

About 10 minutes later, she placed her ear on Madam Gan's chest to check if she was still breathing, and heard a weak heartbeat.

Worried that Madam Gan would call the police, Dewi then decided to drown her employer. She dragged Madam Gan by the hair across the floor to the swimming pool of the house. Along the way, Dewi recalled Madam Gan's daily scoldings and felt angry again. She then slammed Madam Gan's head on the edge of a ceramic tiled step, causing more blood to flow out.

She then grabbed Madam Gan by her pyjamas and dragged her across more steps, causing Madam Gan's head to hit multiple steps on the way down.

On reaching the pool, Dewi then pushed Madam Gan in face down.

Then, she returned to Madam Gan's room and took a pair of her sandals, which she also threw in the pool to create the impression that Madam Gan had committed suicide.

After cleaning up all the blood in the house and changing into a fresh set of clothes, Dewi headed to the neighbour's house to ring the doorbell.

On the way, she met a dispatch rider riding past and asked him to help her, saying her employer was in the swimming pool. The man then called the police.

Madam Gan, a mother of two, was an accomplished pianist and a well-known porcelain artist who regularly donated her works to raise funds for charity. Her paintings included orchids, landscapes and and animals, and she had appeared in society magazines.

She was reported to be the ex-wife of former Hong Kong Legislative Council politician Hilton Cheong-leen.

The autopsy report certified the cause of her death as drowning contributed by contused brain due to a fractured skull.

The pathologist found multiple external and internal injuries, including a V-shaped fracture line of the skull measuring 4cm and 5cm. Most of the external injuries were blunt force injuries caused in the immediate period before Madam Gan died, said the report.

The pathologist also said that the injuries "were sufficient in the ordinary cause of nature to cause death". If Madam Gan had not been thrown into the pool, she "would not have drowned but would have died from her head injuries".

For her offence, Dewi could have been jailed for life and fined.

Correction note: An earlier version of this story said it was Dewi's seventh day of work with Madam Gan instead of the sixth day. We are sorry for the error.