Joe Doherty is a former member of the IRA who spent 23 years in prison, much of it in America fighting extradition, for shooting British soldier Herbert Westmacott in the head. When the cop in the interrogation room asked him if he was sorry for what he had done, Doherty said no.

"I'm sorry, no, not really," Doherty replied. "He's a British soldier. They shouldn't be here. It wouldn't have happened if the British weren't here."

Now 60, Doherty says at some point he stopped thinking of Westmacott as merely a member of an occupying army and started thinking of him as a young man like himself.

"I walk by the spot where he was killed when I go up to Tesco and do my shopping," he told NBC News, referring to the Belfast block where the shooting happened. "I stop and do a prayer for him. For his soul. It's all I can do."

"Was it all worth it?" he asks. "I don't know. Probably yes. And no."

It’s been almost 20 years since the official end of Northern Ireland’s Troubles, and many of the IRA members at the height of the crisis are now, like Doherty, about 60 years old. A new documentary, "When Terror Gets Old," examines these ex-combatants who are now beset by injuries, post-traumatic stress, and poverty and unemployment due to criminal convictions.

"A lot of it was traumatic for people. I remember discussing it with a guy in the yard [at Maze Prison]. He said, 'What am I gonna do with my life now?'" said Sean Lynch, a member of Northern Ireland's legislature who served 12 years for an attempted IRA ambush on a British special forces patrol.

Many "got involved in the struggle at 16. They knew no other life," Lynch said. "People who have channeled energy into politics have done much better, people who got involved in what they saw as a continuation of the struggle."

For the majority, politics means Sinn Fein, the nationalist party once called the political wing of the IRA.

"I look at the TV and they're talking about building business, commerce, hotels," Joe Doherty said of Sinn Fein politicians.

"Once upon a time we were bombing the same hotels. Now we're in government. It's amazing."

Many ex-fighters say they fear for the generation of young people who didn't live through the nightmare of the Troubles and who romanticize the war. In the absence of real opportunity in working class Belfast, they say it may be too easy for young people to slide back into violent sectarianism. Dissuading youths from violence can be a form of community service and personal redemption for many ex-combatants.

Shortly after getting out of prison in 1998, Joe Doherty worked with teenagers in a Belfast youth center, where he was something of a folk hero in republican circles. He says the kids treated him like a celebrity.

His had been a huge cause for the Irish American community when he was arrested in America while working as a bartender after fleeing Ireland. His extradition battle was front page news often.

He went back to the same center earlier this year to give a talk to a group of 15-year-olds and none had ever heard of him.

He still talks to kids, telling them how violence ends in death, heartbreak and jail. Doherty says he watches news reports about kids hopping flights to Syria to join the Islamic State and wishes he could talk to them.

He would tell them that he too was once an angry young man, who felt powerful when he picked up a gun. He would tell them that it doesn't end well and it doesn't get you what you want.

He would say: "I want youse to have an opportunity to make an informed choice. You're gonna come to a stage in life and look back and say, it wasn't worth it."