He did not actually posses a gun. He was arrested for trying to buy a gun.
There was no gun. What was the crime?
Let’s see. Suppose someone in a store tries to put a piece of merchandise in his pocket and walk out, but actually has only stolen an empty box. Is that the crime of shoplifting?
Suppose a man thinks the lump on the bed is his dog, and shoots it, but it’s only a pillow. Crime?
Suppose a man thinks the lump on the bed is his wife, and shoots it, but it’s his dog. Crime?
A decoy policewoman posing as a hooker gets a man to give her money for sex. He’s arrested, she’s not.
A cop solicits a hooker and gives her money for sex then arrests her.
Consider the story of a local police department who set a dummy buck on the side of the road and arrested anyone trying to shoot it for hunting out-of-season.