feeling unsafe in jayanagar because of a stalker

for a bit of a background, this happened in Bangalore, jayanagar 9th block at first we thought it was some guy taking pictures of the building or the moon at night but then we started noticing him again and again and yesterday it happened again me and my girlfriend saw him taking pictures from behind a tree when we were sitting outside her place.

i know how that guy looks and where he lives, what should be my next step to make sure he stops doing what he's doing, considering i know where he lives it won't be hard to know who to accuse for it, but I don't know what kind of proofs i can gather while staying in the legal boundaries, for one i can try recording him behind that tree taking a picture of us or face up to him and chase him down when i see him

i just don't know if these two of my options would be in the legal boundaries.