Imagine this. You're a father with an awesomely gorgeous 18 year old daughter. Halloween night, she decides to go to a party in the hood wearing a G-string and a sexy top. You know the type of guys that will be there. You allow her to go as she is. She gets raped. Are you to blame legally? No, you are not. Could you have prevented the crime by responsibly guiding your daughter’s behavior? Quite probably, you could have.
At least you are logically consistent. I guess you think it is the rape victim's fault.
Your analogy is not even close to the situation though. He left the gun for a specific purpose for his ex-wife and left it in a closet for her.
That's like a woman who is extremely attractive walking around her own neighborhood in her everyday clothing. The guy didn't even "advertise" as you seem to imply when you are blaming the rape victim in your example.