By the time he realised the pocket of his trousers had been slit by a pickpocket, the man sitting next to him on an SBS Transit bus had alighted.
He decided to take the same bus, which runs on a loop service, to go home and change.
Imagine his surprise when the same man later boarded the bus with his alleged accomplice.
Mr K.S. Ng immediately sprang into action to try to apprehend them.
What ensued was a confrontation and tussle between the 47-year-old engineer and the alleged thieves onboard the bus before they managed to escape.
Recalling last Friday's incident at about 9.50am on board SBS Transit bus service number 62, Mr Ng told The New Paper that he had been so engrossed listening to music on his MP3 that by the time he discovered the back pocket of his trousers had been slit, it was too late.
Although his wallet was still in the pocket, $100 in $50 and $10 denominations were gone.
The wallet, too, had been slit.
Mr Ng said the two men had boarded the bus at MacPherson Road.
He said one of them, whom he described as "very tall and obese" joined him in the back row of seats and the other man, who is tall and thin, sat another seat away.
"The plump man fell asleep and leaned against my shoulder. Although I felt uneasy with the body contact, I didn't bother to wake him up," said Mr Ng, who was next to the bus window.
"I was engrossed in my music and was thinking about my work."
He said that it was only after the two men alighted at Aljunied MRT station that he felt something amiss.
He realised the bus was quite empty and thought it strange that the two men would choose to sit beside him.
When he checked his trousers to make sure that his wallet was still there, he was shocked to find a hole in the back pocket.
He was relieved that his leather wallet was still there, but when he checked it, he found all his money missing Mr Ng, who was heading to his office in Kallang, decided to remain on the bus to return home to Hougang to change his pants.
"As it is a loop service, it went back to Aljunied MRT station about 20 minutes later," he told TNP yesterday.
That was when the two men boarded the bus again.
Mr Ng recognised them immediately.
Seeing his opportunity to nab them and recover his money, Mr Ng got up from his seat and walked up to the bus driver.
"I told the bus driver that I had been pickpocketed earlier and asked him to close the bus doors so that the two pickpockets could not escape," he said.