Said the old man, who declined to be named: "I did not smell anything foul emitting from his flat even though I live just next door.
"It was only when the police came to ask me some questions that I was told that my neighbour had died inside his flat."
Miss Salinah Begum, 17, who lives one floor below Mr Ong, said: "When I came home from school just after 4pm, I took the same lift as the police.
"I heard them banging the door loudly before some officers cut open the grille gate."
Another neighbour, who lives next to Mr Ong's unit, said: "I have never seen anyone visiting the old man. He has been living alone for more than 10 years. I am shocked to learn of his death."
Late last year, TNP reported that since 2007, more than 50 elderly people had been found dead in their homes.
To help the elderly who live alone at home - elderly people like Mr Ong - TNP partnered Ngee Ann Polytechnic and Lions Befrienders Service Association (Singapore), to install wireless motion sensors, known as the elderly monitoring system, in 1,000 homes of senior citizens who are living alone.
The project is targeted to raise $1 million to cover the cost of manufacturing and the installation of the sensors.
More than $800,000 has been raised so far.
This article was first published in The New Paper.