Investigators believe an arsonist may have set the fire that destroyed a vacant building early Tuesday. Kenosha Fire Chief Charles Leipzig said firefighters were called to the blaze at 5907 Fifth Ave. at about 3 a.m. The building was among five aging apartment buildings and a rooming house the city purchased recently, with plans to raze them to make way for future development. Leipzig said there was evidence at the scene of “possible arson or incendiary activity” both at the building that was on fire and, possibly, unsuccessful attempts to burn neighboring vacant buildings.