"Searches are being conducted at four premises of IRB in Pune," a senior CBI official said on condition of anonymity without disclosing details.
A year before he was killed, Shetty had lodged a complaint with Pune police's crime branch about an alleged land scam involving IRB chairman Virendra Mhaiskar.
CBI, which was handed over the probe by the Bombay High Court last year, had on October 24 conducted searches at 11 places in connection with the murder.
Shetty was killed as he stepped out of his house on January 13, 2010, at Talegaon Dabhade town in Pune district.
In 2009, Shetty had written a letter to the Pune police seeking protection as he was allegedly being threatened by Mhaiskar.
Shetty had alleged that IRB and its subsidiary companies with the connivance of bureaucrats prepared fake documents to claim ownership of government land.
The IRB group is said to have extended huge unsecured loans to Purti Sugar and Power Limited run by Gadkari. The company had bagged contracts from the Maharashtra government when Gadkari was Public Works Department minister in the state.