FBI agents confiscated records from Pomierski's home and office in June 2010. Last year, the 58-year-old was indicted on corruption charges, and he resigned as mayor.
Pomierski faces up to 10 years in prison when he is sentenced on August 8.
Building Appeals board member John Hennes pleaded guilty in November to conspiracy and making false statements to FBI agents.
The indictment said Hennes collected bribes from a business owner on behalf of Pomierski. Hennes then allegedly entered into consulting agreements with the businessman to disguise the nature of the payments.
The Associated Press contributed to this report.