By Pam Zekman

(CBS) — It’s the biggest case of property tax exemption fraud uncovered by the Cook County Assessor’s Office.

Now, the agency is trying to collect more than $1 million allegedly owed by a company that claimed homeowners exemptions on more than 100 properties.

Owners are entitled to one exemption — only for the home they live in.

To date, the assessor’s office’s erroneous exemption unit has uncovered $41 million in undeserved tax breaks by property owners who did not qualify for homeowners or senior exemptions. Of that, $22 million has been collected.

Assessor Joseph Berrios is trying to collect from Mack Industries, headquartered in Tinley Park, and operated by James McClelland Sr.

The company buys foreclosed homes, fixes them up and rents them out, among other real estate projects under a variety of names.

“A huge case when you really look at what they were actually doing and the amount of money that they actually owed the county,” Berrios tells 2 Investigator Pam Zekman.

The assessor says that between 2009 and 2014, Mack Industries improperly saved $600,000 in property taxes on 113 homes and now owes the county $1.2 million after interest and penalties are added.

“I was dumbfounded. I was totally shocked,” Berrios says of the scope of the alleged fraud.

“I couldn’t believe that this company would be out there taking advantage of the people they were leasing to, trying to use them in their cover-up.”

The assessor says the company used the renter’s names on 113 applications for homeowners exemptions filed in 2009 under a previous administration. The applications all had Mack Industries’ phone number and suspicious signatures, says Jason Pyle, Director of Investigations for the assessors’ office.

He noted that the signatures were in a “pretty unique handwriting” with, for example, looping L’s, C’s and S’s.

On Thursday, an administrative law judge said that based on a visual inspection of the documents the applications were fraudulent. The administrative law judge ruled the assessor could place liens against 75 of the properties to collect the taxes owed, plus interest and penalties when the properties are sold.

Two other companies that bought additional properties from Mack Industries have also been cited in the case for the tax breaks they inherited after they purchased them.

Mack Industries offered no witnesses for the hearings. McClelland did not respond to phone calls from CBS 2. The company can appeal the administrative law judge’s ruling in circuit court.

Meanwhile, Berrios says his erroneous exemption unit has reviewed exemptions for 15 percent of Cook County’s 1.3 million properties and will continue to do so.

“If you want to cheat, then we’re going to come after you,” he says.

People who improperly get tax breaks from exemptions they are not entitled to results in every other property tax payer having to pay more than their fair share, he says.