Should i rat out my sex offender neighbor?

I've been living in a pretty nice apartment for almost 2 years. About 6 months ago a young couple moved into an apartment a couple of floors up directly above me. My building only has like 10 apts in it. Anyways you can hear all kinds of crap through the vents and I constantly hear this couple fighting and physically abusing eachother. This girl is ALWAYS ballin her eyes out and he sounds like he gets pretty rough with her. Its just a mess up there on a regular basis. My motto is usually mind your own buisness unless its gets seriously outta control. So I come home from work last night and open my mail box and there is a card from the sheriffs office with this guys picture on it stating that he is a tier111 sex offender for rape! Now I know my apts do not rent to sex offenders and his last name isn't on the mailbox, just hers. But he is obviously living here and using this address. So now I don't feel very safe. I come home from work late at night and really don't want to cross paths with this dude, especially if they have been goin at it. My question is , would you rat them out or mind your own buisness. My main fear is retaliation. Who knows, if they get booted he may try to find out who ratted on them and do something crazy or whatever. They are not the most mentally stable people in the world. Its crazy, I moved outta the city to get away from a situation similar to this. And here I am again. Anyways thanks for your imput, I'm not sure what to do!