It is worth pointing out that this article appeared in the Baltimore Sun, whic is ideological bastard child of the the New York Times. I seriously doubt these people will be charged unless there is strong evidence to suggest that it was not self defense.
Self-defense, indeed, as a legal defense may not apply unless there is convincing evidence that lethal force was unavoidable and necessary.
This is true for both criminal and civil actions - the latter being, for instance, lawsuits brought for wrongful death by relatives of the deceased.
Otherwise, you can have a hypothetical case where someone, intending to commit homicide, baits someone with premediation into an action that sets up a supposedly "self-defense" scenario that is really a set-up for murder.