Alan's ability to make such a judgment was based on a simple logic: if Sirius wasn't lying, then there were only two possibilities for how Voldemort found James and Lily. One was that the Fidelius Charm itself had failed, and the other was that the Secret-Keeper wasn't Sirius from the beginning.
However, back in his second year when he realized he couldn't contact Lily, it proved they were indeed protected by the Fidelius Charm, and there was no way the spell had been lifted. He also understood that the effectiveness of this protection was absolute; it could not be bypassed by outside rules. Whether it was Legilimency, Veritaserum, or torture, if the Secret-Keeper didn't genuinely reveal the information, the secret remained hidden from outsiders.
That left only one other possibility.
When Sirius heard Alan voice this deduction, his expression became even more pained. He clutched his head with his remaining strength as if trapped in a cycle of self-torment.
"Don't say it, don't make me recall those things. This is all my fault. I failed James and Lily's trust. I chose the wrong person!" Black pressed his head tightly against the iron bars, clearly punishing himself.
"Just as I expected." Alan ignored Sirius's distress and continued to speculate. "Since you weren't the Secret-Keeper, then who was? It had to be someone you trusted implicitly. Within your group, the closest were you, James, Lupin, and Peter Pettigrew. If it wasn't you—and since Peter always seemed timid and fearful—you likely wouldn't have chosen him under normal circumstances. So, was it Lupin? Was he the Secret-Keeper you chose?"
"No," Alan said, shaking his head as he re-evaluated. "If Lupin had betrayed James, you would have pursued him with your life." He recalled the events immediately following the murders and realized the key. "That's right, it was Peter!"
"You switched to Peter as the Secret-Keeper, didn't you? You wanted to deceive everyone, but you outsmarted yourselves. Peter Pettigrew is the real traitor in the Order of the Phoenix, and your choice directly exposed the secret to the Dark Lord. You went after Peter immediately after the attack for this very reason. You were seeking revenge."
The more Alan deduced, the more the series of events felt logical. When Sirius heard Alan speak of this long-buried past, he began to tremble violently and fell silent.
"It seems I was right." Seeing Sirius's reaction, Alan confirmed his theory. "Why won't you defend yourself? The one who truly betrayed the Potters was Peter. You are innocent."
"Alan, you were always far too clever." Sirius's voice was faint, and tears streamed down his cheeks, dripping from his chin. "But if I hadn't suggested changing the Secret-Keeper, and if I hadn't blindly trusted Peter, James and Lily would not have died. I killed them. I am guilty."
"So you would rather be locked in Azkaban than continue to torment yourself outside?" Alan found Sirius's logic incomprehensible. *You think you made a mistake, so you have to rot in a cell?*
"Only by staying here can my guilt be lessened, Alan. Don't worry about me. Let me stay here and atone for what I did to Lily and James," Sirius said through his tears.
"But you are innocent. Locking yourself away is useless. If you truly believe you were wrong, you should be out there making things right. You know there are still many Death Eaters at large; they are all accomplices of the Dark Lord." Alan tried his best to persuade the dejected man.
"I can't even imagine getting out of here, Alan!" Sirius suddenly looked up, his eyes full of despair. "I've been here for so many years and I still can't forget my mistakes. I can't forgive myself. You should leave quickly and let me wither away in this dark corner. This is what I deserve. As for the Death Eaters, I believe in Dumbledore, and I believe in you. Even if I were out there, it wouldn't make much difference."
Alan was rendered speechless. How could someone be so stubborn that they refused to leave prison even when innocent? If Sirius was unwilling to leave, then even if Alan proved his innocence to the world, Minister Bagnold's promise would mean nothing.
Alan continued to plead, trying to entice him with the world outside and the thought of Lupin, his only remaining friend, but it was useless. Sirius buried his head in his arms again, resisting everything Alan said.
Alan turned his head helplessly toward the spot where Minister Bagnold stood. The Minister had not yet recovered from the shock. *Peter Pettigrew was the Secret-Keeper? He was the true traitor?* Bagnold found it hard to believe; after all, to commemorate the "heroic" Peter Pettigrew, the Ministry had posthumously awarded him a First Class Order of Merlin. If this were overturned, the impact would be even greater than the scandal of releasing Sirius.
However, sensing Alan's gaze, Minister Bagnold gave a subtle, supportive nod. Alan thought of one final point that might move him.
"Sirius, what about Harry? Have you just given up on your godson? James and Lily are gone; it's your responsibility to take care of their child! Are you planning to let Harry grow up alone, without any real family?"
Alan reached into his coat and pulled out a magical photo. It was a family portrait taken five years ago during Christmas at the Potter home. He saw Sirius flinch, the words finally hitting a sore spot.
When Alan handed the photo through the bars, Sirius couldn't resist. He reached out and took it, staring blankly at James and Lily, and then at the young Harry held in Alan's arms.