Hmm, it appears that there's definitely a case of possession here, both the eyes and the (unseen) tendrils of red confirm that. We also have what appears to be a link to Bulgaria that needs investigation. I'd hazard a guess that the link is going to end up answering a few questions and generating more.
Some party or parties unknown obviously targeted Ron and/or Hermione and did a fair job of it. In addition to investigating the leads that have turned up, I'd hope the Aurors are looking at both past potential threats and at who might have been "threatened" by something either Ron or Hermione was doing. Once you know it wasn't Ron at his worst, you open up a whole new area for investigation and forensic inspection. I wonder if anyone is going to do a thorough magical inspection of the crime scene and find evidence of those "tendrils"? If Harry happens to stay the night there, will they try and take over him? If so, will his ability to resist Imperius help him deal with the possession attempt? I could see that giving a lead back to the immediate perp, if not the one controlling him/her.
Author's response
As usual, you've made some excellent points here. A great writer and a good friend of mine constantly tells me to create characters that the readers will love and then abuse them. "Make the protagonist "protag"", that's my goal here - the bad news, for the characters, is that they will experience all kinds of abuse along the way. . .