Do officers of the law not shout: "Put your hands where I/we can see them !"
Looking at the photograph of the presumed criminal, it is obvious his right hand is not visible (like suspect no 2), in fact it looks like he might have been
reaching for something on the inside of his jacket.
In a case like that, a policemen would take physical action, he would immediately use force to control the supposed criminal who is not following orders.
So all that is fine, however, standing on the suspects back and giving him a hard kick in the head is not fine.
Standing on his back to keep him down would be permissable, the kick to the head is the no-no here.
This policemen should be punished/admonished/demoted, he was doing his job, but he went overboard.
Unfortunately when you have a brutal crime culture, you also get a brutal policeforce to counter the balance.