Harassment can be difficult to prove
As a crime, harassment can be difficult to prove as we know so well via NFHiB, especially the "lower level" instances, e.g. your 'harasser' being outside when you are outside, watching your every move or behaving unnaturally.
The harassing party will always have some excuse for being there, even if the Police are called for assistance. Often an accused harasser can show distress by claiming "oh no, I waiting for a friend" or innocently claim "you must have the wrong end of the stick!" and so the catalogue of excuses and lies continues.
The perpetrator is very much aware of what they are doing, sometimes it can take the torturous form of a "dripping tap" and at first the "victim" may not be aware of it as this can be extremely subtle. 