Looks to me that something got cut on the arm/upper extermity, for some reaosn stayed at the top of the stares for ~5 mins (maby unconcious?) then made it way (standing) down the stares where it did something for ~10 mins, bleeding the eintire time. then headed out to some other room (the footsteps)
~-~(HDX)~-~
For some reason, I highly doubt this is the case.
Firstly, iago probably wouldn't be talking as lightheartedly as he is about it. Secondly, the clues don't exactly agree with your situation. The way the blood is splattered on the walls would make it impossible for it to be some cut on the arm. If it was any bigger than a cut, there would be a lot more blood on the carpet. Also, it wouldn't take that long for the blood to clot if it was a cut. Bleeding stops (or at least stops -- unless it's a huge laceration) after a few minutes.