Very, very strange neighbor! Any assistance?

Well, last night I was watching T.V. in my apartment. My living room is right near a big window which overlooks the balcony. And I noticed something moving rather fast in the corner of my eye, so I looked to my right and noticed my neighbor whacking off against the balcony. When I looked he didn't even run away. He just kept going and got more aggressive with each stroke. After about 3 seconds I panicked and closed the curtains. Then I ran to the phone to call the police. By the time the police arrived he was already gone. I pointed out his door to police so they could arrest him. The police left and came back about 5 minutes later and said that they think I got the wrong guy. They then said that I could file a police report. But that's it. So I gave them the description and they said that my neighbor definitely wasn't the guy. But I know it was! So anyways. It's over now but I'm kinda afraid to be here now because the police officers never did anything. Any suggestions?