LAKE STATION, Ind. — New court records show that the former mayor of the northwest Indiana city of Lake Station admitted to recording and listening to phone calls of City Hall employees over several years starting in 2011.

The Wednesday filings were part of Keith Soderquist’s presentencing agreement. He is to be sentenced Sept. 28 after pleading guilty and being convicted in two criminal cases.

The agreement reveals that the government learned about the wiretapping after a Lake Station City employee discovered a recording system device in March. An FBI investigation revealed that Soderquist had the system installed during the construction of city hall in 2011.

Records show that between Oct. 12, 2011, and Aug. 13 of last year, Soderquist recorded about 425,000 calls. Since Dec. 1, 2014, he had listened to about 30 of the recordings.

Soderquist admitted to violating the federal wiretapping statute in the agreement. In exchange, the government said it won’t file new charges, but the wiretapping will factor into the sentencing for his two previous cases.

“The system was not installed for eavesdropping,” Soderquist’s defense attorney Scott King said Wednesday. The phone system was installed to improve customer service while protecting city employees against false accusations, King said.

The former mayor pleaded guilty earlier this year to helping his stepdaughter hide more than $16,000 in court bond money she stole from the city by helping her get a loan to cover up the theft. And a jury in September found Soderquist and his wife, Deborah, guilty of using campaign and food pantry funds to gamble at casinos.

He potentially faces 42 months in prison when he’s sentenced on Sept. 28. The government also has recommended that Soderquist pay $3,520 in restitution to Lake Station and $22,571 to the Internal Revenue Service.