Purulia police on Wednesday constituted a special investigating team (SIT) headed by the district police superintendent to probe the robbery at a showroom of a branded jewellery chain in the town on Tuesday.

On Tuesday, eight robbers had entered the gold and diamond jewellery shop in Purulia posing as customers and looted ornaments worth Rs 8 crore at gunpoint. They also beat up the security guards and took away the CCTV hard disc with them.

Two investigating officers of the SIT visited Ranaghat, where a gang of robbers raided a store of the same jewellery chain almost simultaneously, to interrogate the five robbers arrested there after a chase. "We are trying to find out whether there is any link between the twin robberies as the modus operandi of the two crimes was the same. We suspect the mastermind behind the two burglaries is the same," said an investigating officer of the SIT.

The police also found CCTV footage from cameras installed in Purulia's Nampara market area. The footage showed three persons, possibly robbers on a motorbike, hurriedly escaping through the narrow lanes adjacent to the jewellery shop.

"Two of them were holding bags sporting the logo of the jewellery shop. Another motorbike with two youths also hurriedly followed them holding similar bags," said the officer.

Another team of officers will go to Bihar as the police suspect that the criminal gang hailed from the neighbouring state.

"In such crimes in the past, we found the involvement of a gang that operates from Patna. The gang only robs jewellery shops and gold financing companies across the country," said an officer.

The police are also collecting call details from the nearby mobile tower on the day of the crime.

"As Purulia town is close to the Jharkhand border, we suspect they might have fled there," said a police officer.

Inspector general of police Bankura (range) B.L. Meena on Wednesday inspected the shop and spoke to the employees there.

"We got certain information and on the basis of that, we are investigating. The gang involved in the crime will be arrested soon," he said.

In Ranaghat, police estimated that the Bihar-based gang had decamped with jewellery worth over Rs 10 crore. Ranaghat police, however, have been able to recover jewellery worth Rs 90 lakh apart from Rs 3.70 lakh in cash from the five gang members arrested.

Superintendent of Ranaghat police district A. Kannan said: "We have got some leads and are quite hopeful to arrest the entire gang."

The preliminary probe has revealed that the eight-member gang that struck at the Mission Road store in Ranaghat hailed from Vaishali in Bihar. They had arrived at Kalyani three weeks ago and were staying at two rented houses in the Neemtala area of the town in the guise of labourers. The police have detained the house owner for interrogation.

The police have started a probe on the basis of a complaint lodged by Kaustabh Dutta, store manager of the Ranaghat unit of the jewellery chain.

Apart from Purulia cops, a team of Madhya Pradesh police visited the Ranaghat police and checked the identity of the robbers. The cops from MP are probing a similar dacoity in Bhopal.

Employees of the Ranaghat jewellery store staged a silent demonstration urging the police to recover the robbed items so that they could resume sales as early as possible.

"The robbery has come as a big jolt before the festive season. We demonstrated to urge the police to recover the looted jewellery and help us restore normal service at the store," owner of the franchisee Tanmoy Sarkar told reporters.