BALTIMORE — Jon Bernthal once did knuckle pushups outside on the sidewalk.

This unscripted moment happened when the actor with the tough-guy face, 45, was in Baltimore last year working on “We Own This City,” which airs at 9 p.m. Mondays on HBO.

Bernthal was channeling former Sgt. Wayne Jenkins, the disgraced former leader of the Baltimore Police Department’s Gun Trace Task Force. Jenkins, who is often described as a larger-than-life character, oversaw the unit tasked with getting guns off the streets. Jenkins was no Officer Friendly to begin with, and by the time the unit was exposed as corrupt, he and his team left a trail of brutality, corruption and a fatal collision during a high-speed chase in their wake. Jenkins is serving a 25-year sentence for robberies, drug dealing and other crimes.

The Baltimore Sun chronicled the collapse of the GTTF in a 2019 series called "Cops and Robbers." Written by former Sun reporter Justin Fenton, the series was followed by his 2021 book, “We Own This City,” about the entire sordid affair. That led to the six-part HBO miniseries, whose six executive producers include David Simon, another former Sun crime reporter, and George Pelecanos, a Washington, D.C.-based crime novelist. Simon and Pelecanos also worked on “The Wire,” a five-season HBO Baltimore crime drama that ran from 2002 to 2008, as well as shows such as “Generation Kill,” “Treme” and “The Deuce.”

In addition to Bernthal, Baltimore native Josh Charles plays Detective Daniel Hersl, and Jamie Hector plays Detective Sean Suiter, whose 2017 death was ruled a homicide despite questions about the circumstances: he was shot in the head a day before he was to appear before a grand jury investigating police corruption. Hersl is serving 18 years in prison after being convicted of robbery and dealing drugs. Wunmi Mosaku plays Nicole Steele, a lawyer in the U.S. Department of Justice’s Civil Rights Division sent to Baltimore ahead of a consent decree — still in effect in federal court — that requires and monitors improvements in policing the city.

The series begins with Jenkins giving a lecture to a roomful of attentive police cadets. Jenkins captivates them with his seemingly good guy talk of not beating up suspects because it’s bad policing. From there, the episodes detail a crash course in how petty corruption turns into racketeering, stealing and reselling illegal drugs. Ultimately, prosecutors dropped hundreds of cases against defendants that involved the work of the corrupt officers and dozens of lawsuits were filed against the city.

Along the way, the series chronicles the unrest of 2015 that followed the death of Freddie Gray in police custody. Jenkins is seen rallying other officers before clashing with protesters.

Bernthal’s portrayal of Jenkins is nuanced. While Jenkins’ actions are a stain on the police department, he is shown as a husband and father — and Bernthal played a role in getting that other side of the man onto the screen.

“In the original scripts, we didn’t know a lot about Jenkins’ personal life,” said Pelecanos. “Jon came to us and said, 'On one hand, he had all this dirt. On the other, he was a devoted family man.’ We wrote additional scenes at the prompting of Jon.”

Bernthal prepared for the role by going on raids and ride-alongs with Baltimore cops, some of who were former GTTF members. He got to know friends of Jenkins on and off the force, spoke with Jenkins while he was in prison and was in court the day he was sentenced.

“There’s this whole other group who have been victimized, and that’s good police,” said Bernthal.

The wounds from that bad policing remain raw. While shooting a scene of rioting that developed during the unrest, Bernthal’s portrayal of a cop apparently so convinced a bystander that the person tried to punch him.

“Jon was swung at by a passerby. Someone thought they were joining a protest,” said Reinaldo Marcus Green, the director and another of the executive producers. “There’s method (acting), and then there’s Jon. Jon carves out his own lane.”

Bernthal was born in Washington and grew up in Cabin John, Maryland. He studied acting in Moscow before getting his break on AMC’s “The Walking Dead.” Since then, it’s been a barrage of television and movies: “The Punisher,” “Ford v Ferrari” and “King Richard,” which Green also directed. Asked about “King Richard” star Will Smith slapping comedian Chris Rock on stage last month at the Oscars, Bernthal would only offer, “Will’s a friend, and I judge my friends not at their lowest moments but at their highest, and I’m just really sad about the entire situation.”

While he often plays cartoonishly masculine men, the last time he had to be a tough guy in real life was “every time I want my kids to go to bed,” he said laughing.

“I’m enormously interested in exploring all the various components of masculinity. Masculinity has been corrupted by folks who think it’s about being bombastic. I think it’s about being sensitive, open, courageous and openhearted," he said.