As I said before, they are not above the law, but they have different rights, authorities and responsibilities under the law when on duty.
It's not about face, it's about doing his job. How does a policeman defend the public by walking away? How safe would the world be if rather than confront a lunatic with a weapon police simply walked away? What you are suggesting is idiotic.
I'd love a bit of whatever you are smoking.
According to the SCMP, the guy was Nepalese, a HK resident and had numerous convictions for assault and wounding. He might well have gone after the cop if he'd tried to back off.
The cop did his job, I think it's a justified use of lethal force.