Roommate has abandoned belongings and has not paid rent
I live in a 4 bedroom apartment with two other roommates. One roommate's rent check bounced in mid July, and has been AWOL since then and we have no way to reach him. He has not paid rent for the months of July and August (today is August 11). We know he is alive and well, but he will not return our voicemail messages and we do not know where he is living.
He has left all his stuff behind and still has keys to the apartment. We want to get his belongings out of the apartment but he will not come get them. I am wondering what laws pertain to this kind of issue: Can we legally sell his belongings and use that money towards paying the rent? Can he sue us or the landlord? Is there a time frame we need to pass before we can sell his things/throw it out?
Also, because he still has keys, does the landlord have to legally change the locks to our apartment?
Any information with links to legal documents would be very helpful. If it helps, I reside in Chicago, IL.