RE: Are police officers supposed to use all means necessary to stop someone who is running away?
If the one running away is violent and is judged to be a grave danger to the community, yes, the officer has to stop the man.
In the case of Walter Scott, all indicators look like he isn’t one. Also, there’s no need to give chase. The officer has the car and its registration and plate number. They can always find Walter Scott from the information they have.
"Finding the perp later" doesn't work. A perp who resists and runs from a cop in the present will of course do it again later.
That's not to defend Slager's shooting. Just trying to point out what a tough job cops have.