The crew worked with smooth precision, setting up amplifiers, spindly mike-stands, a huge high-tech drum kit with the clustered, shiny look of an oil refinery. Others checked lighting, flicking blue and yellow spots across the stage. At the public entrances, two crewmen from a second bus erected metal detectors for illicit cameras, recorders, or handguns. Especially handguns. Two attempts had already been made on Boston’s life, one at the Chicago Freedom Festival, when Chicago’s Mayor had been wounded at Boston’s side.