I've picked up everything, found every journal, tried to investigate every InvestigationTarget. I've tried resetting game days (after 245 days Susanna's body disappears), resurrecting the body, resetting my level and leveling up once, entering Windhelm from every angle and time of day, talked to Viola and Jorleif, and tried it at every stage of the Stormcloaks questline. I have used console commands to start and end the quest, both inside and outside the city.
I have reset the Windhelm visit count then returned several times at the right time of day. and have never been able to start the quest with that character. I did pretty much the same thing - killed Nilsine, got access to Hjerim with the key from Torva, etc.
