I had been playing through this quest and accused the court wizard of the murders in Windhelm. I went to see him in prison and he told me to look for the real killer at night. I ran frantically around the city but couldn't catch up to the arrow indicator on the map. I did find a dead body though and no one seems to want to acknowledge that it is there. Everyone just walks past it. So, I went to my house and found the real murderer inside, trying to find his bloody altar. I can hit him until he falls to his knees but he gets back up and carries on. If I try to hit him more after he goes down, guards come into my house and start attacking me! I have no conversation options with the Jarl or his steward to tell them the real killer is in my house. How can I complete this quest?