I'll try to keep this short.
The Party of Five leaves The Tavern, following Quest NPC. Suddenly, they are jumped by three bugbears, which seem to have a beef with the Quest NPC. Quest NPC teleports away.
Bugbears attack The Party, which turns out to be a bad idea. Two are put down, the third runs.
As he flees, the Chaotic Good party member attacks him at range, with the intent of killing him. He justifies this with the belief that the bugbear was a threat to the innocent persons of the city.
Are CG's actions justified, or should he be shifted to Chaotic Neutral?