If someone is stealing your bike or car YOU MAY NOT use force to protect PROPERTY. ONLY LIFE. If you are in it or on it while they are trying to steal it and "feel your life is threatened" then you may use deadly force.
I dont think you can shoot them in the back however. Still a non no
Also a mis-conception. If I am confronted by a gunman who has killed a person, I draw my weapon, he runs. I can shoot him dead in the back w/o worrying about reprocussions because i have REASONABLE INFO THAT HE MAY SHOOT SOMEONE ELSE (after all he just did), and I am protected under the law to defend my life as well as those around me.
AGAIN, you MAY NOT use deadly force to defend property unless you are in it and feel threatened.