CHICAGO — New video shows the moment a Good Samaritan disarmed a robber on a CTA Blue Line train Sunday morning before the Chicago Marathon.

As the train stopped at Cumberland, Jean Paul LaPierre stepped off and asked another commuter why marathoners seemed to be rushing for the doors.

“I said ‘this doesn’t seem like the right way.’ He said ‘No, there’s a guy on the train walking around right now robbing people.’ That kind of made me mad,” LaPierre said.

He decided to head back onto the train and confront the man entirely on his own. What happened next was caught on video by a passenger still on the train.

LaPierre grapples with the the robber and hold him against the side of the train, pulling the gun from his hand in the process. The suspect yells at LaPierre to let him go, but he refuses.

“I’m not letting you go! I’m not letting you go! I’m not letting you go!”

In town from the Boston area where he runs a storage facility, the 54-year-old said he’s used to tough guys. Golden Gloves boxing in his youth armed him for this encounter.

“I’m a boxer. I’ll break your head in one punch,” he says in the video.

A marathon runner who was threatened moments earlier said she’s thankful LaPierre was there.

“He didn’t hesitate to step in at all. It was incredible to see; because everyone else just sat there frozen,” she said.

After pulling the gun from the alleged robber’s hand, LaPierre handed it off to another passenger. He said the man had friends on the train who tried to intimidate him into letting him go, but he held on until police arrived.

“They started threatening me but I just stood in his face. The guy kept saying to me, ‘It’s just a gun, let me go, let me go.’ I kept telling him, ‘you’re not going anywhere,’” LaPierre said.

“It don’t matter,” the suspect says in the video.

“It matters to me,” LaPierre replies.

According to police, 30-year old Tremaine Anderson is charged with one felony count of robbery with a firearm.

He has a long history of prior arrests, including attempted robbery, battery and public indecency. A judge ordered him held without bond.

LaPierre said he went on to run his 12th Chicago Marathon. But he also told us, he’s what’s known in the running world as a “bandit,” someone who runs marathons without always registering or paying.

Despite the stand-off on the CTA, LaPierre says he loves Chicago.

“It’s one of the best cities I’ve ever visited. Incidents happen all over. It is what it is, you know?!” LaPierre said.