Firefighters are investigating the cause of an early morning fire Monday that destroyed three school buses and caused an estimated $120,000 in damages. Salem Lakes Fire Chief Mike Slover said firefighters were called to the blaze at 5:55 a.m. The fire started in a bus that had recently been repaired and quickly spread to two other buses in the maintenance area of Dousman Transport Co., 28401 Wilmot Road, Trevor. Slover said the fire didn’t appear to be suspicious and may have started in the electrical system of one of the buses. The Kenosha County Sheriff’s Department said there were no injuries, and the buses were unoccupied at the time of the fire.