Six youths from Bihar who would move around the city at night on hired vehicles robbing jewellery shops were arrested in the city early on Wednesday, police said.

The group succeeded in robbing some stores without a trace. But in some, they fled in a hired vehicle as soon as residents raised the alarm, the police said.

Complaints had been lodged at police stations in Kasba, Haridevpur, Survey Park and adjoining areas since September. On most occasions, the iron shutters were lifted and twisted after one of the locks had been prised open.

Cops had a hard time tracking them down as the vehicle number was different in every CCTV footage, the police said. The registration numbers led cops to car rental companies.

The six were picked up from a flat they had taken on rent in Gulshan colony in the Anandapaur area off the Bypass. Several locks, small instruments made of steel, multiple sets of duplicate keys and a crowbar were seized from them. “They are from Bihar’s East Champaran,” a detective department officer said. “The group targeted small jewellery shops along the Bypass.”

“When we started scanning CCTV images, we found the men would get off a car while its lights were kept on. Usually, four would go out while two would stay at their rented home,” the officer said. “On one occasion, the entire group turned up in two cars.”

The car rental companies are mostly in Anandapur, Madurdaha and along the Bypass, he said. “We have alerted the Bidhannagar and Barrackpore commissionerates to find out if there had been similar break-in attempts by the group in the past,” the officer said.