My one last comment on this topic...having been the subject of public complaints (all unfounded BTW)...the last thing Police would do is deliberately plan to harass the complainer. This alone would add weight to the complainer's story. However, should you witness this person breaking the law, you would not avoid it, but you would make 100% sure that everything you did in the investigation was above board and beyond reproach, knowing what heat would follow.
Police know that it is a common tactic for someone who is the subject of charges to make complaints so that pressure would be applied so that the initial charges were dropped. Some supervisors cave in to the pressure and make the charges go away, others with backbone allow the whole process to come out in open court and lets the chips fall where they may. Some of my bosses caved and even refused to pursue criminal mischief charges against the false complaints, others backed me and followed the whole complaint process, while permitting an impartial Judge decide on the validity of the initial charges.