Suspect: Barty Crouch Jr.

"How dare someone do this in Azkaban..." Sirius Black stared at the bottle of potion on the table. "That's insane!"

Vizet was also studying the bottle of Polyjuice Potion. "Once the effects of the Polyjuice Potion wore off, the person who took it would reveal their original appearance..."

"That person had a very firm will. They intended to die in Azkaban looking like someone else, which was why they prepared so much Polyjuice Potion."

"We have to find him, don't we?" Sirius Black looked at Vizet and Dumbledore. "Since his will was that firm, and he was completely prepared to die..."

"That person was very likely a Death Eater too! Vizet, you saw it in my memories as well. Weren't those Death Eaters exactly like that?"

"Voldemort had clearly fallen, and there'd been no word from him for so many years, but they still firmly believed... that Voldemort would come back to save them."

As he spoke, his brow gradually furrowed. "Since what I ran into when I escaped was a skeleton... it means that person must have been dead for a very long time..."

"To bring Polyjuice Potion with him... and then sneak into Azkaban... he must have had accomplices... I don't know who they were, or where they've gone now..."

"At present, there is only one thing we can be sure of..." Dumbledore said. "The person who contributed the effects of the Polyjuice Potion at least did not find Voldemort."

"Headmaster Dumbledore, you mean..." Sirius Black thought of someone at once. "Because of Peter Pettigrew?"

"Exactly!" Dumbledore nodded, confirming Sirius Black's guess. "In the past two years... he has actually appeared at Hogwarts more than once..."

"Judging from the clues left by his appearances, at the very least, he lacks a stable helper. That is why I believe