> Why did they dig at night in the woodlands? Did he have a permit from the authorities? This isn't something the article discloses at all. It's just assumed he did secure necessary authorizations.

He was doing this to force the authorities hand, to convince them to dig up the tunnel - which is considered a war grave that should not be disturbed.

He did not secure any authorization as that would never have been given to a private person. Archeological team, maybe.