A robber walks into a police officer's home and tries to buy a motorbike as a getway vehicle with the money from the bank he just robbed... sounds like the plot of a joke or the beginning of a comedy skit.
Well, according to This article, it seems like this is just what one person did in Arkansas. Because he paid with the stolen money, after he left, the officer just checked the money and it was easy to pin things down on him.
I am no expert on crime but it does require planning. One certain, Buying a motorcycle from a Law enforcement officer in Uniform after one just robbed a bank sounds like a very risky idea to me.