How should I deal with an animal in the attic?
Not knowing where the house is limits the advice.  However since it has a flat roof, I'm going to assume it's not anywhere where it snows a lot.

You need to get a professional for several reasons.


In most states, as a landlord, you're required to do something and the only way you can demonstrate due diligence with something like this is court is to hire a pro.
Animals carry lots and lots of nasty things, not just rabies (as if that isn't bad enough).  If you trap it you risk injury, if you poison it then at some point you have to remove the carcass and ... gross.
The professional should be up on whatever obscure state and local laws affect removing the animal.


Most importantly, if the pro gets rabies, it's not your problem.  

Edit:  Yeah, I know it a Do-It-Yourself site, but sometimes the right advice is "Don't Do-It-Yourself"