The Bloomfield Police Department is warning residents about a string of thefts involving catalytic converters.

Police say car owners found the items were stolen off their vehicles nine times between May 3-7. On several occasions, witnesses told police they saw three men in ski masks.

Police say the thieves seem to be targeting all makes and models of cars. Some have been parked on the street, while others were in supermarket parking lots.

One theft occurred on Monroe Place. A witness says three men wearing ski masks had an Acura raised up on a car jack. One of those men then apparently got under the car and cut the catalytic converter loose.

The witness told police that the suspects drove off in a Chevy SUV, which was either gray or champagne-colored.

In another case, the thieves targeted a delivery driver at a building along Broad Street. The driver told police he was inside picking up medical supplies and that he left his vehicle for only 18 minutes. The catalytic converter was gone when he came out.

Catalytic converters hook up to a vehicle’s exhaust and turn the vehicle’s harmful toxins into carbon dioxide. They are often targeted for theft because they contain precious metals, including platinum. The part alone can cost $500-$900. Once stolen, the catalytic converters are either sold for cash at scrap yards or used for resale.

The U.S. Attorney’s Office recently reported the arrest of four men who were coming across the George Washington Bridge to New Jersey, stealing the pricey car parts and driving back. Police were able to make an arrest with the help of a witness. The suspects were found with several catalytic converters valued at $5,600.