Waltham's 911 center received a call for a bus fire on Spruce Street on April 27th. Squad 5 and Ladder 2 were dispatched. Upon arrival, they found a camper fully involved. A primary search found no one in the vehicle. Deputy Bob Lahey requested Engine 1 to respond and take a hydrant at Adams Street. It took firefighters about 20 minutes to extinguish the fire. The State Fire Marshal was requested for the possibility of arson.