Totally feel for you buddy.
I had mine keyed 4 times, and it got to the point where I was or felt like I was going mad and paranoid.
I had my suspicions of who it might be but the police weren't interested one bit. So after a year of this happening I finally caught them just by pure luck.
Long story short I filmed him keying the car from front to back, I could have stopped him before he got the chance but I wanted the footage to finally put an end to it.
The look on his face as I opened my front door, camera in hand just as he finished keying the drivers side was pure magic.
In some ways I pity the people who do this and hope one day they will own something which they have worked long and hard for, and then to have it vandalised by a mindless thug.