For the last five months, he witnessed the abuse of a 58-year-old woman, allegedly at the hands of her husband and her daughter.
Living just next door to the woman, he had been hearing screams of "tolong, tolong" (Malay for help) coming from her flat at night.
The man, who wanted to be known only as Mr Singh, 39, decided to secretly photograph the vile acts committed by the pair, using his mobile phone.
He said he had stood outside the flat and pretended to look away while aiming his camera phone at them.
"I was caught once and the husband argued with me, warning me not to show the pictures to anyone," said Mr Singh.
Last evening, he showed The New Paper the pictures. Every image reflected the fear in the woman's desperate eyes.
She had been beaten with two types of brooms on her soles and mouth. She had been stepped on.
Her husband had pulled her hair. Her daughter had even threatened to hurl a wooden stool at her despite her pleas.
Her suffering would have gone unnoticed if not for a 77-second video taken by another neighbour, Mr Mohammad Juani, going viral after it was uploaded on Monday.
It shows the woman sweeping the corridor outside her Lower Delta Road flat two weeks ago when her daughter, 25, suddenly slapped her four times in the presence of Mr Singh's mother, Madam Asha.
So why didn't Mr Singh or his mother report the abuse to the authorities?
Mr Singh, who is unemployed, said: "Every time I threatened to report, they begged me not to."
He said he had lent his neighbour a few thousand dollars about a year ago. It has yet to be repaid.
Madam Asha said she has given up on trying to intervene.
She said: "When I go next door to help, both mother and daughter would tell me to 'mind my own business'. They would shout and scream at me, and I would run back to my flat."
Describing the slapping incident captured on the video, Madam Asha said she had tried to intervene.
"I told her to stop but she continued to hammer her mother," said the single mother.
The old woman and her family had lived in their two-room unit for the last two years, said Madam Asha.
A note left outside their flat, supposedly written by the daughter, said that her father had run away after owing people a lot of money. The mother and daughter were also in debt.
A 26-year-old man said he made a police report after watching the video on Monday evening.
The police, who showed up at the flat after 8pm on Monday, confirmed the report.
Neighbours reported seeing the old woman being taken to hospital, accompanied by her daughter.
"She is 58 but she looks like a grandmother in her 70s," said Madam Asha, adding that her neighbour appeared to have aged following the alleged abuse.
The woman had a crew cut in the video but Madam Asha said it had nothing to do with the abuse. After discovering she had lice, the woman agreed to let her daughter cut her hair short.
Mr Singh said he has heard the old woman using vulgarities on her daughter and calling her names, sparking the almost-daily fights.
On Monday, Mr Juani uploaded his video clip on Facebook, under the name ApohTecky Numero. It immediately sparked outrage among netizens and prompted the authorities to act.