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DALLAS (CBSDFW.COM) – As a tough-as-nails Texas lawman who brought serial killers to justice, Parnell McNamara’s life inspired a role in the Jeff Bridges film “Hell or High Water.”

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McNamara is the sheriff of McLennan County. He grew up in the area and, prior to becoming sheriff in 2013, served as a U.S. Deputy Marshal for 33 years out of the Waco division. He comes from a long line of law enforcement officers. His grandfather, his father and his brother, Mike, all wore the U.S. Marshals badge.

“People say, ‘How did you become a U.S. Marshal?’ I have to admit, I just kind of inherited the job,” McNamara said.

McNamara started with the Marshals in early 1963, when he was in the 11th grade. His father was the sole Deputy U.S. Marshal in Waco, and would need guards from time to time. He got permission from the U.S. Department of Justice to use his two sons as help.

The McNamara brothers idolized their father. “We always looked up to our father. He was 10 feet tall to us. He wore the big pistol, and was just the quintessential Texas lawman. A true blue law enforcement officer,” McNamara recalled.

Today, the sheriff’s office reflects that history. McNamara displays old badges, hats and saddles around the wood-trimmed office. “I took the sheriff’s office back to the western look. Put the old gun racks in, like in the old sheriff’s and U.S. Marshal’s offices,” he said.

And then there are the guns themselves. In a case on the wall, McNamara displays an impressive collection of antique firearms. Among them is a 1928 Thompson submachine gun — with “Tommy Gun” stamped on the side from the factory. Nearby is a powerful 10-gage shotgun that belonged to his father.

Even his mother, at 95 years old, felt at home on the gun range. “She would cut loose, her machine gun, little white hair flowing,” McNamara laughed.

As a marshal, McNamara and his brother tracked down bad guys. His most memorable case was the pursuit of serial killer Kenneth Allen McDuff. They tracked McDuff to Kansas City and helped bring him back to Texas to face the justice system. “In November of 1998, I witnessed his execution. He never apologized. He was brutal and evil to the very end,” McNamara recalled.

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It was a job that he never wanted to leave, but knew would come to an end. Federal law enforcement officers are required to retire at age 57. “There’s a standing joke that there were claw marks on the carpet of the U.S. Marshals office where they had to drag me out,” McNamara said.

McNamara learned about “Hell or High Water” in 2015. His cousin, Taylor Sheridan, wrote the script. He knew that Sheridan was writing a story about Texas lawmen, but didn’t know that he would inspire the part until that spring. “He said Jeff Bridges would be playing that part. I was very flattered and very honored, because I’m a big fan of Jeff Bridges. I think he’s a really good man and a wonderful actor,” McNamara said.

“Hell or High Water” is the story of two bank robbers chased across the West Texas landscape by a Texas Ranger on the brink of retirement.

McNamara knew that Bridges wanted to get into character. The two had phone conversations about how to pull off the look and the dialect. “I said, ‘Jeff, you don’t want a stupid-looking hat, or you’re going to look like Howdy Doody.’ He said, ‘Well, I don’t want to look like Howdy Doody.’ I said, ‘We don’t want you to look like Howdy Doody!” McNamara laughed.

He remembers one conversation with Bridges, where the actor asked how McNamara would deliver a line. “He asked me, ‘How do you talk to someone after you retire, and you still try to get them to confess to a crime?’ I said, ‘Jeff, you have to change your tone of voice and approach it from a different way. You no longer have that big hammer to hang over their head like you do when you’re carrying a badge,” McNamara said.

The actor and the inspiration met in Austin over the summer, at the movie’s red carpet premiere. “All of a sudden, I’m standing there by Chris Pine, and Bridges is down the way. I’m answering questions and it was so cool. They were all so down to earth and put me at ease. I never felt intimidated by them. I was kind of one of the guys. They really made me feel good,” McNamara said.

McNamara added he has no plans to become an actor at 70 years old. He’s also not ready to retire, though he lost his brother — his best friend — last year. “I lost my brother. I lost my partner of a lifetime. We were partners all through school, college and law enforcement,” McNamara said.

McNamara is happy going to work as sheriff every day. He feels fortunate to have a career in law enforcement spanning nearly 50 years. “I’ll probably just fade away as an old sheriff, you know?” McNamara said.

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That may be a while from now. For Texas sheriffs, there is no age limit for retirement. “As long as I can. As long as the people of this community want me to be in there, and as long as I’m able to do it,” McNamara said.