This is a theory I came up with when I first visited the sanctuary on this play through, you hear one of the assassins talking about, well actually it was Gogron gro-Bolmog who said it, he says:


"I once saw Lucien deal with an insubordinate Brother, someone who had broken the Tenets. It took me a week to get the blood off my boots."

And you can see this guy walking around.

http://elderscrolls.wikia.com/wiki/Dark_Guardian

Now what if, and bear with me here, this guy was the one who broke the Tenets and as punishment was cursed to guard the sanctuary forever? The guild doesn't seem above such a punishment and might very well do this, hey this guy is walking around for a reason as a undead corpse and we never hear anything about him, so thought it could had been a little easter egg or something for that what might happened if you break the rules. Your thoughts?

It′s an interesting theory if anything