He saw a man allegedly steal $300 at the scene of Saturday's accident.
Mr Ling Lek Onn, 57, went to Bukit Merah West Neighbourhood Police Centre yesterday morning to give details of what he saw.
The cleaner told The New Paper on Thursday evening that he was waiting at a Rochor Road bus stop on Saturday morning when he heard a loud crash.
As he ran to the scene, a tall man of average build was ahead of him.
The white-shirted man stared for a moment into the taxi, walked around to the front of the vehicle and knelt on the ground.
Then he picked up three $100 notes from the ground, stuffed them into his pocket and walked off, Mr Ling said.
"I don't know if he realised I was there, although he glanced once behind him as he stood up," he said.
"The moment he took the money, he didn't look at (the cabby and his passenger) again. I didn't get to see his face."
Mr Ling said he was not sure whose money it was, but thinks it could have belonged to cabby Cheng Teck Hock, 52.
He said only one other person was there at the time and this person called for the Singapore Civil Defence Force (SCDF) and the police.