Clearly not, the person that knowingly modified it to do something illegal is at fault. Preventing anyone from modifying anything is a backwards response to the real problem: the guy that wants to do the illegal thing.
Zero, as long as the person:
(1) Knew it was loaded
(2) Voluntarily accepted to receive the gun.
In this analogy the gun going off broke a law. So you voluntarily handed somebody a loaded gun - who then committed a crime with that gun.
Obviously context matter - but you can bet the police will be asking why you gave that gun to them.