Theory history: Submitted 2015-06-19, Debunked 2016-01-15
I believe that the player is Kara from the Covert Front series and that Mur might be Karl Von Toten from the same series. At the end of Covert front, Toten is working on a contraption that looks to be the coordinates device from the loop episode, and escorts Kara through a door that is projected on a wall through light. This light device is eerily similar to what happens in the Subnet, and could be an early pioneer for what the Kent Lighthouse does. When the light was destroyed by Kara when she threw a crowbar at it, she effectively trapped herself and Von Toten in the Submachine, which was then primitive. We do not know how life works in the Subnet, and the possibility of time itself not passing while Kara makes her way through the world is quite possible. In addition to transfering between realms such as the basement and ancient sections, she could be traveling through time as well. If this is true, then Murtaugh may not be dead after all.