Monday night's installment of Kurt Sutter's Discovery docuseries "Outlaw Empires" (10 p.m. ET on Discovery) profiles the South Boston Irish Mob, and tells the story of legendary gangster Whitey Bulger, who was arrested in 2011 as one of the most wanted fugitives in America after a 16-year manhunt.

Sutter interviews Bulger's former criminal associate Kevin Weeks, who describes the brutality and fear Bulger used to take control of Boston's criminal underworld in the 1970s. "The fear people had of Whitey became one of his most valuable assets. The violence that he did commit served a purpose. In order to maintain order, there had to be some sense of enforcement," Sutter says in the exclusive clip below.

In an interview with HuffPost TV, Sutter described how devastated Weeks was when he learned that Bulger had been serving as an FBI informant for years before he disappeared in 1995.

We talk to Kevin Weeks, who was one of Whitey Bulger's [lieutenants]. And the most fascinating thing about talking to that guy is that he's not angry, he's not remorseful, he's fucking heartbroken. He's fucking heartbroken that Whitey ended up being a paid informant for 10 years. He's truly forlorn. You just realize how much that was this guy's life. It was like a brother or father turning on him. So to me, those are the characters that you go, 'Oh man, you can't fucking write that, you can't make that shit up.'

"Outlaw Empires" airs Monday nights at 10 p.m. ET on Discovery.