Why is a Crystal Lake medical office full of unopened mail, but no employees?

Katie Duda noticed an unusual $500 lab test from a provider she said she never heard of on an Explanation of Benefits letter she recently received from her insurer, Blue Cross Blue Shield of Texas.

"Had I been frequently to the doctor getting labs, I probably wouldn't have even given it a second thought," said Duda.

So, she and her mother traced the lab, Niyraa LLC, to a strip center in Crystal Lake and found an office with a sign on the door saying to drop off mail inside. The door was unlocked. No employees were anywhere in sight.

Thinking that was strange, they reached out to CBS News Chicago to take a closer look.

Five times over several months, CBS News Chicago reporter Marissa Sulek and photographers visited Niyraa LLC. They found thousands of pieces of mail, mostly from various Blue Cross Blue Shield entities, addressed to Niyraa LLC sitting in U.S. Postal Service bins on the front desk.

We contacted Crystal Lake police, the FBI and U.S. Postal Service Inspectors to tell them all of that mail was there and people's personal information could be at risk.

But every time we went back, the thousands of envelopes were still there. The only thing that changed was that they moved from the front desk to the back, now stuffed in a growing pile of black and white garbage bags.

So, who's behind this medical office and what's going on with all of the mysterious mail?

"Mohammed I Quadri" is the name plastered all over the lab's signage outside, inside and on current lab certifications framed and hanging on the wall.

Brittany Serby, who owns the Functional Wellness Clinic a couple of storefronts down, said she's never seen Quadri and is concerned about what might be going on with all of the mail inside the unusual office.

CBS News Chicago contacted the mall owner, who said he hasn't seen Quadri in months, but Quadri still pays the rent.

We also tried several ways to contact the mystery man. We emailed, texted, made phone calls and went to addresses we found that might be connected to him. No luck.

We even waited outside the Crystal Lake lab office one weekday for hours, during a time when it should have been officially open for business. He never showed.

We couldn't find Quadri, but what could really be going on inside this mysterious office with no employees ever around?