When does self-defense become a crime?

A convenience store clerk in Richmond was charged with manslaughter after defending himself during a robbery at a convenience store where he worked.   How did self-defense become manslaughter?

Obviously, I don't know the details of this case.  My theory here is that the Mr. Simmons was charged with manslaughter because he fired several shots at Mr. Harris outside of the store while he was running away.  Your claim of self-defense ends the moment the threat on your life stops.  In this situation, Mr. Simmons should not have followed the bad guy outside of the store and he certainly should not have kept shooting.  If Mr. Simmons had stayed inside the store and called the cops, I do not think he would have been charged at all - even if Mr Harris had died from the injuries.