The Illustrated Guide to Criminal Law
Chapter 8: What Have You Done?
Page 9: Transferred Intent
So if Joe intended to hurt Simon, but then accidentally hit him with his car, even though he caused the harm and had the right intent, he did not commit the act with that intent, and so he is not guilty.
Joe backing over Simon in his car, saying “oops!”
Now what if Joe meant to main Simon, and threw a brick at him, but missed and maimed Mamie instead?
Brick missing sauntering Simon and striking a woman in the back of the head. Nearby barbershop quartet (including Average Joe) sing “He missed and maimed Mamie instead!”
If Joe previously made his desire to harm Simon public, and then runs him down in the street, how hard a time would he have proving it was an accident? When a guy runs over someone he’s been ranting about hating on facebook (for example), I can easily see a prosecutor thinking it’s more than a coincidence.
If Joe had previously and publicly threatened Simon, then I’d imagine defense would probably go for a plea deal on that one (even if it was in fact an accident), unless there’s some kind of hard scientific evidence that it couldn’t have been on purpose. No jury is going to believe that it was a coincidence if there was a prior threat.
Until we have mind-reading devices, proving mens rea will always be about making reasonable inferences from the available evidence. If A harms B, then a prior threat from A to B is powerful evidence of mens rea.