I've done numerous playthroughs and I've never really had a problem with this quest. But on my recent character, I decided to buy Hjerim after I had started the quest. I bought it, then went into the house and did the investigation portion. Now the quest says to follow up on the evidence found. If i remember correctly, I now need to go see Violo Giordano (spelling?). Only problem is that she is no where to be found. Can't find her in her house or in Candlehearth. Also it seems that I can't upgrade Hjerim yet. Has anyone run into this problem, and if so is there a fix?

Buying the house before completing the Ice and Blood quest seems to break the quest. You will have to reload before you buy the house.