It's always someone you fucking know. I was robbed quite a few times when I was younger and it always turned out to be a "friend" or roommate. It was right after I had $25,000 worth of music equipment stolen that I decided it was time to live alone.
Thats fucked up! Man I completely feel for that frustration!
The answer is to not live alone, but live with better people! I live with heaps of other students, mostly low income, but we help each other out. Nothing has ever been stolen in memory here.