By Charlie De Mar

CHICAGO (CBS) — Mario Casciaro was wrongfully convicted of murdering his coworker – in what remains one of the biggest unsolved cases in McHenry County.

Now, as CBS 2’s Charlie De Mar reported Monday night, Casciaro is using his experience to make sure it never happens again.

When he spoke with De Mar on Monday, Casciaro was dressed in a sharp suit. But that was not always the case – just four years ago, he was wearing jumpsuit at Menard State Prison.

Casciaro had been sentenced to 26 years in prison in the 2002 murder of his 17-year-old coworker, Brian Carrick.

But Casciaro walked free after his murder conviction was overturned, serving about two years of his sentence.

“I don’t think that I’ll ever forget what happened, or forget what a day in the life of the inmate is,” Casciaro said.

It’s that mindset that motivated Casciaro to go to law school. He graduated from Loyola University Chicago.

De Mar: “Did you have any doubt that this day would come?”

Casciaro: “I did not. It was just a matter of when. I felt that my calling is to fix these miscarriages of justice and be a zealous advocate for those that don’t have a voice.”

Last week, Casciaro found out he passed the bar. He is becoming an attorney, just like he told the late CBS 2 reporter Mike Parker he was going to do days after his release in 2015.

“I’m not an angry person,” Casciaro said back then. “I just want to help prevent this from happening to the next person.”

Carrick’s body has never been found, but his blood was located in the cooler of a McHenry County grocery store owned by Casciaro’s family. Prosecutors at the time said the motive was a drug debt owed to Casciaro.

But a key witness, Shane Lamb – also an employee at the store – changed his testimony, and the Illinois Appellate Court tossed the case.

“I don’t think any other attorneys in the country can actually look at their client and say, ‘I’ve been exactly where you are right now,’” Casciaro said.

Casciaro did receive a $50,000 settlement from the McHenry County State’s Attorney’s office, and currently has lawsuits pending against the Village of Johnsburg and the City of McHenry.

Charlie De Mar