Wormtail
Father broke out of his Imperious Curse, he was wandering on the grounds raving, I had to take care of him. No one suspects a thing.
And you know what the best part is? That fool inspector was walking by while I did it! I tried to talk my way out first, of course I did, our Master doesn't want any disruptions that might be caused should the Inspection Inspector be called, but he was mocking me again! I asked him what he was doing, and he said "why taking a hike of course my good man, would you like to join me? Perhaps we could inspect together, as inspecting friends." YOU SEE? HE KNOWS! HE KNOWS EVERYTHING!
I had to take care of him I did! Besides, if there's one disappearance there might as well be two.
I haven't killed him yet though, I'm awaiting the Master's orders, I transfigured him into a rock and put him in the trunk that I keep Mad Eye in. They should keep each other company.
I hope Master isn't too mad, after all, it might be good to get an insider in the ministry's inspection game, we could shut Hogwarts down in a heartbeat.
Waiting for further instruction.
The Dark Lord's Favorite