CHICAGO (CBS) — Northwest Side Alderman John Arena has helped police crack a case of hundreds of stolen catalytic converts that has been frustrating drivers all summer.

CBS 2’s Suzanne Le Mignot reports on how the suspects were caught in this original report.

In the last several months, police say there have been hundreds of catalytic converter thefts on the Northwest Side. Residents in the 16th and 17th police districts have been hardest hit.

In July, 45th Ward Ald. John Arena noticed two men out early in the morning.

“One of them got up from underneath the car, put a small sawzall into a bag,” he says. “I asked if they stole a catalytic converter actually. They said no.”

“They started running to the car and I just ran up to the car as it was taking off, took the license plate down.”

Arena’s quick thinking helped lead to felony theft charges to be filed against two men last week.

Donzel Jenkins and Melvin Griffin were caught by police on patrol at Racine and Belmont Thursday. Sources say Jenkins is believed to be one of the ring leaders in the thefts.

Police saw Jenkins go into a backyard carrying a sawzall. A check of his car, revealed seven catalytic converters. At the time of his arrest, Jenkins was on parole for theft.

“Feels weird in your gut, make the call. It’s worth it,” said Arena.

Mechanic Pedro Garza, at Victor Mufflers in Mayfair, says he’s been incredibly busy replacing stolen catalytic converters.

“I want to say about 25 last week,” said Garcia.

He said they are valuable because of the zinc, gold and platinum inside.

Police are now investigating what scrap yards are buying these catalytic converters. Each one sold nets the thief more than $100