I bet you it was a rifle because if it was a handgun he would aim to the side of the head 
Besides rifle or not it proves it can be done 
Well, we'll never know, all we know is it was a 'low calibre weapon' and I don't think it was denied that it was possible. However, in your example only one shot would have been fatal, both shots would have killed Sheila - the first just wasn't immediately fatal.