The National Forensic Service has released its assessment of the deadly bridge collapse at the Sejong-Anseong Expressway that killed four workers and injured six others.

The investigation team handling the case at the Gyeonggi Southern Police Agency said Wednesday that it received the results of the assessment, which showed that a launcher became unstable and a girder toppled over due to the lack of a structural review for a back-feeding operation.

Police say the accident occurred during the process of pulling out the beam launcher, a device used to lift and install girders, backward.

The forensic service concluded that the equipment was operated without the necessary checks to ensure stability before the bridge collapsed on February 25.