It, however, did not specify if it was a bank locker or a locker at residence.
"We feel this could be a tip of iceberg and many more things could be revealed during the probe," said a CBI officer.
The agency also found documents pertaining to five properties. "We knew that Kumar possessed these properties, but the documents were found today in the locker," the officer told PTI.
CBI arrested Kumar on August 18 for taking bribe through an agent for clearing a regional film.
The trio will be produced before the special CBI court tomorrow and the agency is likely to seek extension of their custody.