 After the scam came to light in May, the CBI interrogated Pawan Kumar Bansal, Congress MP from Chandigarh, for ten hours, but failed to find substantial evidence to nail him.In his statement, Bansal denied having any knowledge of his nephew's activities.CBI does not have any tapped conversation which shows that former Railway Minister Pawan Kumar Bansal was involved in or had any knowledge of the Rs 10 crore cash for post bribery scandal, which prompted the agency not to make him an accused in the case, sources said here today.