Yup. There was a 'Watchtower' pamphlet left on my doorstep yesterday. When I left my house, I saw several Jehovahs Witnesses canvasing the neighborhood. No one could 'prove' it was they who left it on my doorstep. Gee, for all I know, it could have been my Baptist neighbor, right?
Would that level of evidence allow you to convict someone of murder?