When he entered the room, his mother looked as if she was sound asleep.
But when Mr Zhuo Jun Kang, 24, called out to her, Madam Wu Bao Mei, 42, did not respond.
That was when he realised, to his horror, that she was dead.
The Singaporean accounts clerk had died under mysterious circumstances - she had no visible wounds on her body.
Their home in Kluang, Johor, did not have any signs of a struggle or forced entry.
But her jewellery, other valuables and car were missing.
Malaysian police have classified the case as murder and are looking for a man to help with investigations.
Malaysian newspaper Guang Ming Daily said the neighbours had noticed a man leaving Madam Wu's double-storey house on Tuesday afternoon.
Mr Zhuo, a bird's nest distributor, said: "Mum was still asleep when I left for work that morning.
"When I sent my sisters home that day, her car was not around. I thought she had gone out."
They could not enter the house as he had left the keys at his workplace. So the siblings drove to the company to retrieve the keys.
When he called her mobile phone earlier, she did not answer. But he was not concerned because she usually ignored calls when she was busy at work.
It was only when Mr Zhuo returned home with his sisters at about 6.30pm that he made the shocking discovery.
"She was under the blankets, with pillows all around her. I found the position weird so I decided to check on her," he said.
"That was when I found that she was not breathing so I immediately called the police."
The room was dark and the air-conditioning was on.
He later realised that valuables like her gold chain, ring, handbag containing money and his youngest sister's mobile phone were missing.
Madam Wu had initially settled in Batu Pahat, also in Johor, with her husband, now 50.
She moved to Kluang around 10 years ago after they separated. The elder Mr Zhuo works in a furniture company in Singapore, Guang Ming Daily reported.
Her four children - a son and three daughters - lived with their father until they moved in with her about six years ago.
Madam Wu had a history of high blood pressure.
Chinese evening daily Lianhe Wanbao also reported that the Malaysian police are not ruling out other possible causes of death.
This article was first published on JUNE 27, 2014.
Get The New Paper for more stories.