I don't know that simply asking a person to drop charges or not testify would qualify as tampering. However if that person were threatened directly, or indirectly, with a smear campaign, or other forms of punishment, should they proceed, would that qualify? How about if the person(s) who approached or confronted with requests or demands were turned down and followed up by systematically contacting the friends, family, colleagues, church, employer, potential employer(s), etc, with allegations, facts, rumors, or implications meant to harm or destroy that person's relationships, employment, and standing in the community? Would that be considered tampering, or some other actionable offense?