Gilderoy Lockhart seemed to think he himself had made the attacks stop. Hermione overheard him telling Professor McGonagall so while the Slytherins were lining up for Transfiguration. "I don't think there'll be any more trouble, Minerva," he said, tapping his nose knowingly and winking. "I think the Chamber has been locked for good this time. The culprit must have known it was only a matter of time before I caught him. Rather sensible to stop now, before I came down hard on him."