There is a law in LA, Louisiana Statute RS 14:225, which makes institutional vandalism a crime, and it was specifically intended to deal with defacing of schools, churches, and other institutions with hate symbols--Given that decorating a tree with toilet paper is considered an act of vandalism, it is certainly arguable that hanging nooses in a tree is an act of vandalism as well.

A different prosecutor might have interpreted the law much differently than Mr. Walters did. Perhaps, if he had known that this would become a national issue, he would have interpretted it differently, as well.