The Hells Angels motorcycle club protected its turf through murders, bombings and general terror, federal authorities say.

Gabriel Grchan, meanwhile, grew up in the Quad Cities with less interest in law enforcement than numbers. He “fully expected to be working for a public accounting firm” one day, he said.

So he didn’t exactly expect to help take down Melvin Chancey, the onetime president of the Hells Angels’ Chicago chapter.

Nor did Grchan expect to be where he is today, serving as the special agent in charge of IRS Criminal Investigations in Chicago. He started the job in April — right around tax time — and oversees about 100 agents in a field office that covers all of Illinois and Indiana. His agents help investigate tax fraud and other financial crimes.

Meanwhile, a search is underway in Washington, D.C., for a new U.S. attorney who will “stop the violence in Chicago.” And the Chancey investigation that Grchan participated in is an example of how the IRS’ criminal investigators can help take down a violent gang, whether it’s the Hells Angels or the Hobos.

In an interview, Grchan said, “At the end of the day, the large organizations are going to be dismantled through the financial investigations.

“Eventually, they’re going to want to spend their money,” Grchan said. “These are crimes of profit. They’re crimes of greed.”

Grchan grew up the son of a county sheriff. He didn’t see himself following in his father’s footsteps, but his dad introduced him to agents anyway. Eventually, Grchan landed a job with Chicago’s IRS field office, and he became one of the case agents in the eight-year Chancey investigation.

By 2005, Grchan was among a handful of federal agents slated to testify against Chancey, records show. If the case had gone to trial, Grchan might have found himself on a witness stand explaining how the Hells Angels used dues, special assessments and other sources of income to pay for its clubhouse and club members’ legal expenses.

Instead, Chancey pleaded guilty.

Hugh Mundy, an associate professor at The John Marshall Law School who’s a former federal public defender, said such a gang prosecution is typically a “multi-agency effort,” and it’s the IRS’ job to chase the money. Ultimately, it tries to figure out where the gangs are sending their cash and “cut them out at the knees” by disrupting their funding stream.

After investigating Chancey, Grchan was the assistant special agent in charge in Phoenix and later the special agent in charge in New Orleans, where his office helped prosecute former New Orleans Mayor Ray Nagin, working with the FBI field office led by Michael Anderson. Anderson is now the special agent in charge of the FBI in Chicago.

“I think that it was just another example of strong partnerships that we have,” Grchan said.

He said he also wants to stay ahead of the latest developments in cyber crime, pointing to “dark web” prosecutions involving the underground website Silk Road.

Cornelis Jan “SuperTrips” Slomp, an online drug dealer who admitted he sold more illegal drugs than anyone else on the Silk Road, was prosecuted in Chicago and sentenced to 10 years in prison in 2015.

An IRS criminal investigator in Chicago was also recently recognized, along with a task force officer from the Cook County state’s attorney’s office, for a multi-year, multi-agency investigation that targeted people selling drugs through dark web sites that allowed them to mask their identities. Thai Walker was sentenced in April to six years in prison in the case, and Paula Walker was sentenced to five years.

“I think that that’s an area that’s definitely going to be our focus,” Grchan said.

READ MORE: Ex-Outlaws biker boss speaks out, sees trouble with Hells Angels, Nov. 27, 2016