An armed robbery of a U.S. postal carrier helped police begin to unravel a crime ring that has stolen numerous muscle cars and other expensive vehicles from auto plants and dealerships in the Detroit area.

When officers caught the man suspected of robbing the postal worker outside Cleveland, they found three high-priced stolen vehicles at his home — a Ram 1500 TRX, a Land Rover Range Rover and a Dodge with a Hellcat engine, The Associated Press reported last week.

That led to federal indictments in June against four Ohio men on charges of conspiracy and interstate transport of stolen vehicles.

One of the men told the FBI that he and another defendant communicated through Instagram with people in the Detroit area about obtaining stolen vehicles, prosecutors said. They said thieves also sold the vehicles, originally worth $50,000 to $100,000, for $3,500 to $15,000 to buyers in Chicago, Indianapolis and cities near East Coast shipping ports.

Investigators say the thieves started the vehicles using hand-held electronic “pro pads.” Many are Dodge Charger and Challenger Hellcats — “the fast ones,” said Sgt. Jerry Hanna with the Macomb Auto Theft Squad in Michigan. “If a patrol car gets them, they are not stopping, and they’re faster than patrol cars. They’re 150 mph all day.”

Thieves also have hit several Ford plants in Michigan, stealing F-150 Raptors and Mustangs.

At a suburban Detroit dealership last year, thieves crashed a Ram through a glass wall then drove other cars in the showroom out through the same hole. Police found a Dodge Durango SRT Hellcat taken after the driver smashed into a brick wall trying to get away. Three other vehicles were later recovered as well.

Jeff Schneider, general manager of the dealership, Szott Chrysler-Dodge-Jeep-Ram in Highland Township, said employees are now using an “old-school” method to discourage thieves — parking boots.

“It’s a deterrent that works amazingly,” Schneider told the AP. “We put boots on all the Hellcats.”