Then he says (new chapter):
"We need to find her," said Dumbledore. "Professor McGonagall, please go to Mr. Filch at once and tell him to search every painting in the castle for the Fat Lady."
"You'll be lucky!" said a cackling voice.
It was Peeves the Poltergeist, bobbing over the crowd and looking delighted, as he always did, at the sight of wreckage or worry.
"What do you mean, Peeves?" said Dumbledore calmly, and Peeves's grin faded a little. He didn't dare taunt Dumbledore. Instead, he adopted this oily voice that was no better than his cackle.
"Ashamed, Your Headship, sir. Doesn't want to be seen. She's a horrible mess. Saw her running through the landscape up on the fourth floor, sir, dodging between the trees. Crying something dreadful," he said happily. .
"Did she say who did it?" said Dumbledore quietly.
"Oh, yes, Professorhead," said Peeves, with the air of one cradling a large bombshell in his arms. "He got very angry when she wouldn't let him in, you see." Peeves flipped over, and grinned at Dumbledore from between his own legs. "Nasty temper he's got, that Sirius Black."
Hope this helps and let me know if you need more,
Professor Dumbledore sent all the Gryffindors back to the Great Hall, where they were joined ten minutes later by the students from Hufflepuff, Ravenclaw and Slytherin, who all looked extremely confused.
"The teachers and I need to conduct a thorough search of the castle," Professor Dumbledore told them as Professors McGonagall and Flitwick closed all the doors into the Hall. "I'm afraid that, for your own safety, you will have to spend the night here. I want the Prefects to stand guard over the entrances to the Hall and I am leaving the Head Boy and Girl in charge. Any disturbance should be reported to me immediately," he added to Percy, who was looking immensely proud and important. "Send word with one of the ghosts."
Professor Dumbledore paused, about to leave the Hall, and said, "Oh, yes, you'll be needing..."
One casual wave of his wand and the long tables flew to the edges of the Hall and stood themselves against the walls; another wave, and the floor was covered with hundreds of squashy purple sleeping bags.
"Sleep well," said Professor Dumbledore, closing the door behind him.