As Judge Richard J. Sullivan wrote in a 32-page opinion, “An individual’s participa•tion in a lawbreaking group may, in appro•priate circumstances, be strong circumstan•tial evidence of that individual’s own illegal conduct,” but no matter the circumstances, “an arresting officer must believe that every individual arrested personally violated the law. Nothing short of such a finding can jus•tify arrest. The Fourth Amendment does not recognize guilt by association.”