CBI has booked former Maharashtra Home Minister Anil Deshmukh over corruption allegations.
The probe agency also carried out searches at various locations in Mumbai on Saturday.
Corruption charges against Deshmukh were levelled by ex-Mumbai top cop Param Bir Singh.
CBI had carried out preliminary enquiry on Bombay HC orders to look into the allegations.
Officials said CBI got enough prima facie material during enquiry to start a formal probe.
CBI has registered an FIR against Deshmukh under the Prevention of Corruption Act.
After lodging case, CBI started a search operation at a number of locations in Mumbai.
On March 25, Param Bir Singh filed criminal PIL seeking a CBI probe against Deshmukh.
Singh claimed Deshmukh had asked cops including suspended Sachin Waze to extort money.
Singh had made the revelations after he was transferred as Mumbai Police Commissioner.
Deshmukh, who is an NCP leader, resigned from the State cabinet on April 5.