Go easy on the matusi there. These are resourceful young trailblazers.
That aside, is there anyone who seriously believes this was not an inside job? If you have seen a 30 meter hole, it's not child's play.
It was certainly a "neat" idea and very much in keeping with the times we are in ... just another version of going underneath the bank and walking away with
gunias full of cash. Also, no violence or threats of violence seen to have been involved; and the bank most likely has insurance for the loss.
Other than the length of the tunnel, one would need a good idea of where the vault is, some knowledge that the floor underneath was not six feet of concrete, etc.