The clip I saw didn't show the shooting.  He was surrounded by police officers pointing guns at him... he started towards the left side of the screen and so perhaps they shot him because he wouldn't throw down the weapon and get on his knees with this hands up? 

I would say that the police, like anyone, has the right to kill in self-defense, or in the defense of others.  I suppose he could have thrown the knife at one of the officers.  If he was running away he could have been a threat to someone else... 

It's not as though I saw a video clip of a man too far away from the cops for him to be able to throw a knife at them or anyone else.  And I can't see the shooting itself. 

In fact, I couldn't even see the knife he was supposedly holding.