Investigators say the cause of a fire in downtown Waterville that destroyed one building and damaged two others remains undetermined. Sgt. Tim York of State Fire Marshal’s Office said Monday that the fire originated on the third-floor deck of the Main Street building, but he says damage was so severe that identifying the cause is difficult. York tells the Morning Sentinel, a sprinkler system in the building had been turned off but he did not know why. The fire started around 4 p.m. Friday and destroyed the top two floors of the four-story building. The rest of the building was damaged by water and smoke. Fire Chief David LaFountain says the investigation had been slowed because state fire officials were responding to fires in Lewiston.