SINGAPORE - The passenger of a taxi who was arrested and charged with robbing the cabby of $500 after the taxi driver made a police report, has been acquitted after a trial.

In a written judgment released this week, a district judge said that he found the testimony of cabby Foo Boon Thye "less then impressive" as he had "materially contradicted his evidence about how he was allegedly robbed" .

On the night of Sept 18, 2014, Mr Foo, 41, stopped his empty taxi along Jalan Bukit Ho Swee to return a phone call. Suddenly, the front passenger door opened and Mr Lim Poon San, 42, got into the front passenger seat.

The cabby claimed that Mr Lim had robbed him. At first, he claimed that Mr Lim had threatened to poke him with a sharp pin-like object which made him hand over $500 in fear.

But cross-examined on the stand, the cabby admitted that Mr Lim never threatened him with such an object. Instead, he said that he handed over the money - two days' earnings - because Mr Lim had uttered threatening words.

Mr Foo said he felt threatened when Mr Lim put his hand into his trousers pocket as he presumed that the passenger was trying to take something out.

After Mr Foo changed his account, the prosecution amended the charge to one of robbery by uttering the threatening words: "You don't want to give me, right? You don't want to give me right? Okay."

However, Mr Lim denied robbing the cabby. He testified that he had boarded the cab asking for a free ride to the Institute of Mental Health (IMH) as he was feeling depressed but was rudely rebuffed by Mr Foo.

Mr Lim, who has a history with the IMH, said he showed the cabby his report and asked for help to go to the hospital as he did not have enough money for the fare. He said Mr Foo scolded him and told him to go away. Mr Lim claimed that he did not ask for any money or threaten the cabby in any way.

In his judgment, district judge Eugene Teo said that the prosecution's case rested on the court finding that Mr Foo's testimony was "unusually convincing" but "we instead have a witness who could not even maintain a consistent stance on the central point in dispute: that is, on how the alleged robbery took place".

The judge said he could not discount the possibility that the robbery charge was being "trumped up" by Mr Foo.

Mr Lim's lawyer Gino Hardial Singh, assigned under the Criminal Legal Aid Scheme, had made the suggestion - which was denied by Mr Foo - that the cabby made up the allegations to get back at Mr Lim for hurling vulgarities at him before slamming the taxi door.

The prosecution has filed an appeal against Mr Lim's acquittal.