Board Thread:General Discussion/@comment-24323037-20140701074655/@comment-65.93.197.237-20140703230610

Here's the reason for his existance, found on Malborn's page:

"This "fake" Malborn seems to exist solely if Roggvir survives his execution for too long. In this case, Roggvir will be moved to this Cleanup Cell to be killed by the "fake."

Kinda creepy, but it's a different NPC, and I guess you'll find Roggvir here if you saved him at his execution, and had already killed fake Malborn.