The CBI on Monday questioned relatives of Trinamool Congress MP Abhishek Banerjee in connection with its investigation into the multi-crore coal pilferage case.
The central agency had on Friday issued a notice to Ankush Arora, husband of Menaka Gambhir who is the sister-in-law of Banerjee, for questioning in the illegal coal mining case.
The agency also asked Gambhir's father-in-law Pawan Arora to join the investigation.
"Both have appeared before the anti-corruption branch officers at CBI's Nizam Palace office here for interrogation," a source in the agency said.
A CBI team had on February 23 visited the residence of Banerjee and examined his wife Rujira in connection with the case. The agency also examined Rujira's sister on the previous day on the same matter.
Abhishek is West Bengal Chief Minister Mamata Banerjee's nephew.
"When Gambhir was interrogated by the CBI, she had told the sleuths that her husband and father-in-law were in the knowledge of some bank transactions. She claimed that she was not aware of anything," the agency source said.
Earlier, searches were conducted at the residences and offices of people who are "considered close to Anup Majee alias Lala" -- the main accused in the coal scam.
Majee is believed to be involved in the illegal coal mining in the Asansol-Raniganj belt of Eastern Coalfields Ltd and has been evading arrest. The CBI has also issued a look- out notice against him.
The investigating agency on November 28 last year carried out a massive search operation in a number of locations in four states -- West Bengal, Bihar, Jharkhand and Uttar Pradesh - after registering a case against Majee.
The CBI is keeping a close watch on businessmen who have a close connection with Majee, the agency source said.
The Enforcement Directorate, another central agency, is also probing the money laundering aspect of the case.