Their last known victims were Cheli Ram and his wife Radha Rani, who were stopped by the gang in Satya Niketan in south Delhi while returning home after a morning walk.
The "policemen" stopped them at a near desolate spot and related a concocted story of a woman who lost her jewellery and was stabbed while walking.
And to gain their confidence, they stopped a man who was passing by - who actually was an accomplice - told him to take off his jewellery, and then returned it to him wrapped in a newspaper.
Now they asked Radha Rani to take off her jewellery too. Using the sleight of hand, they quickly pocketed her jewellery and returned to her a set of artificial necklace and bangles also wrapped in a newspaper.
By the time the horrified couple realized they had been cheated, the "policemen" had gone missing. The distraught husband and wife later sought the help of the real Delhi Police.
Giving these details, Deputy Commissioner of Police B.S. Jaiswal said here Monday that four members of the gang had been arrested.
He said the first arrest was made Saturday and the others were caught Sunday in Rohini in west Delhi.
Jaiswal identified the criminals as Mohammed Ibrahim, 40, Sikander Ali, 27, Nizam Ali, 33, and Sarfuddin, 32.
All of them are from Maharashtra, and had worked there as drivers and electricians, he said.
A few months earlier, police had busted another gang which used the same modus operandi to commit the same crime.