It’s not like they know their way around these tunnels. They were built to be hard to navigate and built to conceal people and contraband.
Bottom line bud, if there was a fire anywhere near a shaft, heavier-than-air gases will sink downward into tunnels. Have you ever heard stories about someone goes down even into a root cellar or something and then passes out, and three more people go down after them one a time and all succumb?
You’re attributing to malice what is easily explained by basic physics and coincidence.