Police and fire investigators remained on scene Friday investigating the downtown fire that started at Mio Posto at 2:30 a.m. on Thursday and burned for hours, damaging adjacent buildings. Firefighters found heavy fire in the kitchen of the Italian restaurant at 68 Putnam St. and put it out but discovered the flames had spread to the attic and to an adjacent vacant building on 30 Caroline St. Representatives from the city building department and code enforcement unit are also investigating to determine the structural soundness of the damaged buildings.