Government investigators combing the country’s top investment banks this week may never find hard evidence of collusion in the underwriting business, but circumstantial evidence of uniform fees in the industry alone could form the basis of a formidable price-fixing case, antitrust lawyers say.

It’s highly unlikely the government will obtain the kind of smoking gun used in earlier high-profile, price-fixing matters — for example, the hours of taped conversations provided by a company insider in the Archer Daniels Midland lysine case.