According to a report from The Associated Press, investigators believe a mechanical problem is to blame for a hayride crash at Harvest Hills Farms on Saturday that killed one and injured more than 20 people.

Citing Sgt. Joel Davis of the state fire marshal’s office, The AP notes that investigators are working to identify what sent a 1979 Jeep down a hill and into a tree, spilling a trailer full of people onto the ground, into trees and into each other.

“It appears there was a mechanical issue and the vehicle could not stop. The operator attempted to stop the vehicle, but could not. That’s when it left the roadway,” Sgt. Davis said, according to WGME.

Investigators are reportedly looking at the total weight of all the riders to figure out whether the trailer was overloaded.

The crash, which took place in Mechanic Falls, Maine, killed 17-year-old Cassidy Charette and injured 22 others. CBS 13 reports that four people remain hospitalized as of Monday morning.

CBS 13 points out that hayrides are not licensed by the Pine Tree State. As a result, there are no regulations or required inspections for vehicles towing people or the trailers they tow.