The CBI on Wednesday detained a TMC councillor, who is known to share close ties with arrested party strongman Anubrata Mondal, following a search operation at his residence here in connection with the probe into the alleged cattle smuggling scam, an agency official said.

Biswajyoti Bandyopadhyay, whose name had cropped up during investigation, was detained for questioning early in the day, he said.

CBI sleuths also simultaneously conducted searches at residences of two other local TMC leaders who are "closely associated" with Mondal and are suspected to have played a vital role in the scam, the official said.

"Names of these three persons had come up during our investigation. We need to find out what were their exact roles and how much they benefitted from the scam," the CBI officer told PTI over phone.

Several documents have been seized during the raids, he said, without revealing much detail.

"We are talking to these people to find out relevant information about their involvement. We are verifying the documents that have been seized," he added.

Mondal, the TMC's Birbhum district president, was arrested on August 11.