Fire investigators on Tuesday were still trying to determine the cause of an early-morning fire on Oct. 10 that destroyed an apartment building on Congress Street and caused minor damage to a neighboring building. The fire at 201 Congress St. was reported around 12:30 a.m. It was a three-alarm fire, according to Deputy Fire Chief Scott Thomes.  He said approximately 20 residents got out of the building and three firefighters were treated for minor injuries.