There's a lot going on during a shooting. Hitting a moving target that small at that distance while under stress and a serious time crunch is far easier said than done. I'll echo General Zod's sentiments. If you have the luxury to shoot them in the leg, then your life probably wasn't in immediate danger. It would be hard to justify that shoot. Shoot them center of mass, or don't shoot them. That'll hopefully keep you out of prison.
As far as the shooting in the leg thing, I wouldn't recommend it. There's a good chance they'll bleed out long before the ambulance even gets there.
Everyone has their own opinion of what they would have done in this situation. But since none of knows if the perp had turned around with a gun in hand or not, which I will go out on a limb and say he didn't, but we don't know for sure. I believe the shooter didn't think about anything but stopping the perp. I also think that, from the angle of the gun, he was shooting at center mass. I also believe that the shooters life wasn't threatened and he should not have fired at the perp.
'You have shown the lower torso but not the upper torso. If you had, you would see the heart, lungs, kidneys, stomach, aorta and other organs that would kill and/or bleed out before he could arrive.
I'm not trying to argue about what should or shouldn't have been done. My statements are mine and only mine.