AUBURN — Vandals cut emissions-control devices from four buses housed at a Merrow Road depot Friday night, police said.

Deputy Chief Jason Moen said Tuesday that detectives had made no arrest but were working on leads. The four catalytic converters were valued at $3,700, Moen said.

It wasn’t the first time that’s happened, said Sandy Buchanan, general manager at Western Maine Transportation Services. In February 2013, vandals stole five of the devices, she said.

Although the company has roughly six of the gasoline-fueled buses, those targeted this year were equipped with electronic lifts.

“That’s very problematic,” she said. “These are very important to people who have mobility issues.”

Weekend ridership is generally lower, so the effect on ridership wasn’t as great, she said. On Monday, a “higher-volume day,” she said, “it took a lot of moving vehicles from some of our rural areas into the city. We weren’t able to do quite as many, but we covered probably 98 percent of the rides.”

The new catalytic converters arrived Tuesday. By late afternoon, mechanics had re-equipped three of the buses with the devices and were working on the fourth, which was expected to be completed by Wednesday, she said.