His mistake was firing warning shots. Very dangerous (you don’t know where those shots will land). A first shot to center mass of the intruder still facing forward would have simultaneously ended the threat and short circuited prosecution.
He probably broke the law. I doubt he’ll be convicted.
Still. If his first shot had been for effect, he would have avoided a lot of hassle.
“His mistake was firing warning shots.”
I think his real mistake was this:
“The detective says Rutter began to run and the son-in-law fired in his direction, striking him.”
I have no problem with shooting a fleeing felon in the back, but it might not sit well with a jury.