So let's get this straight, he was still holding a knife and lying face down on the ground. The hand holding the knife was tucked under his body. The police were trying to get both of his hands behind his back so they could handcuff him.
Except one of the hands was still holding the knife. To avoid the policeman being stabbed whilst trying to get the hand (holding the knife)
behind his back the police shouted for him to "drop the f'ing knife". In order to incapacitate him the policeman kicked the terrorist in the head twice.
Now what intrigues me is what are your motives in seeking to make out a man who has just stabbed two British Jews as a victim?