I'm renting out a bed room in my own 4-bedroom house. This is the first time I'm being a landlord. How do I do proper background check of new tenants and reduce my risk that the person is a criminal?
I am a realtor. For our rental business, we use a service that offers a background check. It costs us about $25, and it is passed along in the form of an application fee.
I suggest you contact a local real estate agent who you know does rentals. Have a conversation about what you are doing, and see if they will help process the application for you, for a fee of course. If you are truly concerned about your safety (The text you wrote can either read as true concern or sarcasm. Maybe we are really in a wild country?) It's worth even a couple hundred bucks to screen out a potential bad roommate.
If you can find a tenant by networking -- co-worker, friend of a friend, etc. -- rather than openly advertising, that often gives you a better pool.
Side advice: Check what local housing laws apply to renting a room rather than having a housemate. Once you start advertising this you may be subject to fair housing laws, additional code requirements, and so on.