Ch. 79 After the aurors come get Hermione for the attempted murder of Draco, Harry is in the Headmaster's office:

Severus seemed as passionless as ever, sitting in a small cushioned chair beside the Headmaster's desk. The old wizard stood terrible and upright by the still-burning fireplace, robed in black like a starless night, radiating power and dismay. All her own thoughts were of utter confusion and horror. Harry Potter sat on a wooden stool with his fingers gripping the seat, and his eyes were fury and freezing ice.

After a lengthy discussion of the case, Harry leaves:

Even as Harry Potter left the room for his own investigations...

But there is no reason to believe he left Hogwarts. Dumbledore then retrieves the Weasley twins from Divination class and gets their map:

The old wizard smoothed the map, bent over it, and whispered, "Find Tom Riddle."

I'd previously assumed that no information came of this, because the Defense Professor was being detained at the DMLE at the time, but Dumbledore almost certainly saw the map report Harry as Tom Riddle.