I can only suggest you try what I suggested, upload the pic to your desktop, open it in any picture viewer and magnify. It really is impossible to tell what his facial expression is.
I would have thought the reasons for not shooting the dog were obvious. Firstly the Palestinian woman was standing (not that she had much choice) right next to it, and there would obviously have been a risk of shooting her by mistake. Secondly, such dogs are trained to grab 'suspects' by the arm firmly (to prevent use of weapons) but without causing any serious damage. That is what happening here. There was no need to shoot it, indeed releasing her from the dead dog would be as hard as releasing her from the live one - and the dog might even bite (rather than just grip) much deeper in death.