Conditional

I heard this sentence in a documentary: "If I shoot you, this is a crime. If I expose you to toxic products, this is legal. But which is the difference?". Is this correct??

Thanks

What is the difference, not which.

Also, I would write "it" [is a crime] instead of "this." But that could be a matter of style. The "which" I consider incorrect.

I'd be interested in knowing more about this documentary!

In the great majority of cases, it's true that "If I shoot you, it is a crime."  Two exceptions (and there may be more): (1) I shoot you in self-defense, or (2) I'm a prison employee in a state/country where capital punishment is allowed and I carry out your death sentence by firing squad.

"If I expose you to toxic products, it is legal."  Hmmm... this is more problematic. 

• If I merely open a jar of something that's toxic, that's not a crime.  It may be a stupid thing to do since we both could be inhaling the fumes.
  
• If I throw the contents of the jar at you, that's considered a crime.
  
• If I (as the head of a major corporation) expose you (the general public) to toxic products, that's definitely a crime.