A Hong Kong taxi driver who overheard a conversation between his two passengers about their plan to cheat an 81-year-old woman has helped foil a scam attempt, leading to the pair’s arrest in the latest of a string of “guess-who-I-am” phone deception cases.

Police on Friday said the 39-year-old driver learned of the ruse through a conversation he heard between the two suspects while taking them to a bus stop in Sau Mau Ping on Wednesday afternoon.

After the two men left the taxi, the elderly victim arrived and handed over HK$7,000 (US$899) to one of them. The driver, who remained at the location, witnessed the transaction and called police.

He followed the pair in his vehicle as they walked away, before officers arrived and arrested the two suspects.

Acting Chief Inspector Lo Yip-wai of Sau Mau Ping Police Station said the two men were detained on suspicion of obtaining property by deception – an offence punishable by up to 10 years in jail under the Theft Ordinance. He added that the money had been recovered.

He said the investigation revealed that the elderly woman, who lived in Tuen Mun, earlier received a call from another man who had impersonated her relative.

“The caller claimed he was her grandson, saying he had been arrested by police and needed bail money for his release,” Lo said.

The woman was instructed to go to the Sau Mau Ping bus stop to hand over the money to someone there.

Lo said the investigation showed the two suspects were members of a triad-controlled fraud syndicate.

The racket had a “clear division of work” with some members assigned to the task of calling their targets while others were responsible for collecting money and acting as lookouts, he added.

The investigation was still under way and further arrests were possible, he said.

As of Friday afternoon, the two men, aged 39 and 49, were still being held for questioning.

Lo said the investigation suggested triad gangs were behind some of the latest phone scams, which had become a new source of income for the groups.

“Guess-who-I-am” scams usually involve swindlers pretending to be a relative of a victim or a friend in urgent need of money.

Scammers will contact victims by phone and ask them to guess their identity. Once the target mentions a name, the tricksters then pretend to be that person and come up with a plea for money.

Between January and September this year, police handled 780 cases of “guess-who-I-am” phone deception with losses totalling HK$58 million.