I have a renter who paid a deposit, took possession of the keys and signed a 1year lease but now is talking about backing out and not moving in.

Even if you don't have keys you can still take possession back.

Investors, homeowners and mortgage brokers found committing occupancy fraud possess a few basic commonalities;Homeowners who claimed OO when in fact it was intended as a rental occupied by a tenant from the start.Homeowners who claim OO but instead have a family member occupy the residence in their place.Investors who claim OO to get lower rates when in fact they have a primary residence elsewhere.Mortgage brokers who falsify records in order to obtain loan approval from the lender.You claimed I have "publicly admitted to committing fraud."

My new tenant would like to take possession of the premises, with their signed lease in hand and change the locks (the bad tenant is letting homeless people sleep inside at night).

ALL of your personal assets and possessions are now exposed and are at risk.

@Andrew Schultz I hope this will helphttp://beta.biggerpockets.com/files/user/kp1/file/release-of-rights-of-possession

Anyone with Ohio Law knowledge can you answer if a tenant takes possession if he moves in his stuff but doesn't sleep there?  

@Ben Leybovich, When you say seasoned does that mean that a period of time has to elapse after he takes possession of property?

Can you write loans secured with property if the lender has physical possession of the deed? 

The title/escrow company makes sure that the property cannot change possession without a clear title.4.