LITTLETON (CBS) – Police are warning car dealerships about an organized ring of thieves stealing catalytic converters right off of parked cars, sometimes by the dozen.

It happened at Acton Toyota in Littleton, where 30 to 40 were stolen this week. Police say all together they’re worth thousands of dollars.

“The bolts that attach the catalytic converters to the exhaust system were just laying on the ground, one by one,” says Littleton Deputy Police Chief Matthew King.

He says surveillance cameras didn’t pick up any activity because the thieves were working underneath cars, out of view. He says detectives have been in touch with recyclers and scrap metal dealers, but none have admitted to buying that many brand new parts recently.

Since the incident, King says he’s heard from many other police departments that have had similar thefts. He says they may all be the work of an organized traveling ring. “All the New England states, Rhode Island, New Hampshire, Maine, so it definitely is a chronic problem right now,” he says.