I’d think you (or a friend/relative/local hitman) should address this directly with the person if you feel safe to do so, be firm and tell him it is not on, and what you want him to now do/not do and that the police will be advised without notice to him should it ever happen again.
I’d also advise the OC of the situation in writing and ask how they can help you (or if you can, tell them what you require them by law to do – as a minimum it is likely breaking a by-law).
Having others aware of the situation will allow others to look out for you and may bring out others who have a similar situation, or can further enlighten you as to the person’s motives – he might be a known creep or a misguided mentally disabled person – who knows for sure?
I’d also document the goings on so you can as appropriate take it to the police.
All up, it seems a sad imposition if you are forced to move by the actions of another tenant so see if it’s possible to fix it great, if not, you might be right in moving. All the best, C.