Hanoi police have announced the arrest of another suspect in the capital's huge petrol scam, which investigators broke up last week.
Nguyen Tuan Quang, 31, was alleged to have supplied an illicit electric chip to 54-year-old Nguyen The Loc, who ran the Tu Liem District station, police said.
The owner told police he bought the chip at VND9 million (US$471) from Quang.
Further investigations have revealed, however, that Quang was Loc's employees.
According to police, the old man paid Loc nearly VND3 million ($157) a month to maintain the chip system.
Loc was taken into custody last Wednesday after his station was found to be fleecing customers by modifying its pump systems with an electric chip.
According to investigators, Loc earned about VND1,200 (S$0.06) extra on every liter of fuel he sold, which was the largest illegal markup detected so far in Hanoi.
Police said that Loc confessed to having installed the chip in May which allowed him to pocket an extra VND15 million ($785.75) per month.
Police said they will continue to investigate the matter.