The federal investigation that prompted Gov. Bill Richardson of New Mexico to withdraw his nomination as commerce secretary offers a rare glimpse into a long-simmering investigation of possible bid-rigging, tax evasion and other wrongdoing throughout the municipal bond business.

Three federal agencies and a loose consortium of state attorneys general have for several years been gathering evidence of what appears to be collusion among the banks and other companies that have helped state and local governments take approximately $400 billion worth of municipal notes and bonds to market each year.

E-mail messages, taped phone conversations and other court documents suggest that companies did not engage in open competition for this lucrative business, but secretly divided it among themselves, imposing layers of excess cost on local governments, violating the federal rules for tax-exempt bonds and making questionable payments and campaign contributions to local officials who could steer them business. In some cases, they created exotic financial structures that blew up.

People with knowledge of the evidence say investigators are not just looking at a few bad apples, but also at the way an entire market has operated for years.