CHARLOTTE, N.C. -- Charlotte-Mecklenburg police are trying to stop a ring of thieves who take part of the exhaust system that is bringing high prices on the black market.

“It's right in the center of the car, the pipe that connects the engine to the muffler. The catalytic converter is right in between,” said Becky Mulholland.

Mulholland didn't know much about catalytic converters until someone stole hers right out from under her sport utility vehicle. She only discovered it was gone when she started the SUV up.

“It was very loud. It sounded like a Mack truck,” she said.

“When you start your car and it sounds like a freight train, you know you've been had,” said car dealer Spiro Balaouras.

Balaouras knows that sound all too well. Thieves have cut the catalytic converters off more than a dozen cars at his small dealership on Independence Boulevard.

“It takes probably less than 15 seconds for them to do it. What they use is an electric saw and literally they can be cut just like butter in just a few seconds,” he said.

He's hardly alone. Thieves cut their way through the fence around a car lot nearby and took even more catalytic converters. Police said the same has happened to cars in parking lots all over the city, and what was once an unusual crime has become an epidemic.

“And they'll go in there and take 15 or 20 a pop in a night,” said Officer Brent Helms.

Helms said what the thieves are actually after is the small amount of platinum inside the converter that's enough to bring pretty big cash at scrap yards.

“They'll get about $200 a piece for a catalytic converter that's cut out from under your car. It's in the muffler system,” Helms said. “No questions asked.”

Helms said the cuts are clean and quick -- the work of professionals. In many cases in Charlotte, police said they believe it’s the work of one organized group.

They have a large file on the man who they said heads up that group. Officers arrested Charles Hall last month after a standoff with Special Weapons and Tactics officers at his home.

Investigators said they found car parts and evidence that Hall had sold $30,000 worth of catalytic converters to scrap yards.

But Hall was released from jail two days later, and police said the catalytic converters are still disappearing.

So too is the patience of some of victims.

“Probably altogether this loss was around $3,500 in one night,” Balaouras said.

He said he isn't sure what more he can do to protect his car lot, and Mulholland won't leave her car anywhere anymore.

“I mean, if I go shopping in a mall, I'm going to think twice, or anywhere,” she said.

Police said they are watching parking lots more carefully, particularly along Independence Boulevard with all of its car lots. But they said it's impossible to watch them all and to keep thieves from hitting again and again.

Also, police in the Steele Creek Division of Charlotte are working with several businesses to engrave catalytic converters with vehicle identification numbers so that police can trace them when they show up at scrap yards