A gold necklace encrusted with 97 diamonds that was stolen from a central Calcutta workshop last month has been found several feet under the floor of a Hooghly house belonging to a diamond broker who operates in Mumbai, police said.

Sheikh Mannan, who works in Mumbai’s Zaveri Bazaar, has been arrested and charged with masterminding the theft by planting an associate in the workshop as an employee. The necklace, recovered on Wednesday, is believed to be worth Rs 50 lakh.

On a tip-off, the police arrested Mannan from outside Calcutta airport sometime after he returned from Mumbai on Tuesday night. Mannan took the police to his home in Guptipara, about 90km from the heart of Calcutta, officers said.

Police sleuths used a crowbar to dig a hole in the floor and pulled out a plastic container. The necklace was in a polythene packet inside the container. Police sources said the workshop owner, Prashanta Mal, had identified it as the stolen necklace.

The man who allegedly stole the necklace for Mannan is still at large, the police said.

An officer said Mannan stole jewellery across multiple states by planting his men in gold and diamond workshops.

He said that Shakil Hussain, Mannan’s alleged accomplice at the diamond-setting workshop in Girish Park, got the opportunity last month to handle the 97-diamond necklace.

“A diamond merchant had engaged the workshop at Sarkar Lane in Girish Park to fit diamonds and polish them for him,” joint commissioner (crime) Murlidhar Sharma said.

“Hussain did the fitting-and-polishing job and stole it on August 23. The workshop owner had no details about Hussain except his phone number. He said Hussain had started working there only a month ago.”

Tracking Hussain’s phone number, the police found he was in touch with a man named Sheikh Mannan in Mumbai. It soon became apparent that Shakil was working at Mannan’s behest, Sharma said.

Preliminary investigations suggest that Mannan used to sell the stolen jewellery at Zaveri Bazaar, Mumbai’s jewellery hub, the police said. They added that Mannan had links with Gujarat’s diamond workshops as well.

An officer from the detective department’s anti-burglary section said the police had received information that Mannan had stolen jewellery from at least three other workshops.

Mannan faces charges of criminal breach of trust by employees and criminal conspiracy and faces up to seven years in jail if convicted.

“As Hussain carried out the theft, the mother case of criminal breach of trust by employees will be against him while Mannan will face charges of criminal conspiracy for the mother offence,” a police detective said.