The Troy School District in Joliet, Illinois has been hit by thieves cutting catalytic converters from school buses before. District officials assumed installing cameras, enhanced lighting, and adding more locks to the yard gates would detour thieves.

However, a routine inspection done by a driver revealed nearly their entire fleet of buses was missing catalytic converters after a single night.

District officials told FOX 32 that 30 buses, or 90% of the total fleet, were vandalized. Without catalytic converters, the buses are considered inoperable. Since most of the buses were handicapped, the district called for an emergency e-learning day.

Almost 4,000 students were learning from home on February 10 due to the district’s inability to get a majority of the student body to school.

The letter to parents noted their efforts to protect the buses from thieves were in vain, and the district is “collaborating with Joliet Police and local authorities, conducting a thorough investigation and ensuring those responsible are brought to justice.”

The district also noted it’s working with its bus vendor to “expedite repairs and restore our bus fleet to full operational capacity at the earliest opportunity.”

Police think it only took thieves an hour to steal 30 catalytic converters

Security cameras the district installed showed a black SUV parked near the yard at 2 a.m., and it was seen leaving around 3 a.m. Police aren’t sure if multiple suspects are involved, and are asking the public for help to identify them.

Catalytic converters are easy targets for thieves, who seek the precious metals inside them—platinum, palladium, and rhodium—and their high values on the black market. Buses have ground clearance, and the parts can be cut with a simple battery-powered saw in just minutes.

Catalytic converters also can’t be tracked, making them particularly attractive to thieves. Unfortunately for the victims, though, new parts aren’t cheap to replace and usually have to be welded on to avoid replacing the entire exhaust system—which can cost thousands.

Hopefully, the district will look into shields, underbody protection, branding, or security cables to keep their school buses operating.