No quibble with most of your statements which are quite logical and reasonable. He wasnt coming out alive. But we do have choices on how to execute someone. What one hears on the audio is not reason and logic as you stated but a mob wanting to burn him alive. That is what i object to. A hail of bullets or even a massive bomb would have been more humane than fire.
If he were indeed still alive prior to the fire, why didn't he surrender peacefully?