Was Sirius Black's innocence always known to Dumbledore?

Question

There are some small details missed in the Harry Potter series, especially as they translated to the films. A lot of them involve Harry's Godfather, Sirius Black...

In the film, The Prisoner of Azkaban, the Ghost-Portrait of the Fat Lady was seen to be slashed, to which she said it was "Sirius Black!" Even Professor McGonagall seemed to presume his guilt as the one who betrayed Harry's parents (without any significant proof).

I could understand maybe Sirius trying to get to Harry in the Gryffindor dorm to warn him, but not why he (as a former Gryffindor himself) would slash at the painting. Granted, the book was set up to keep the suspense and suspicion up so as to keep interest, and naturally, the film follows that pattern. But a lot of the actions don't really make sense; once Dumbledore was aware that Black escaped, if he suspected the man's innocence, wouldn't he have tried to find him himself, or aid him in getting a message to the boy?

So does that mean that Dumbledore wasn't aware of the likelihood of Sirius's innocence before that book?

Answer 1

This is not explicitly mentioned in the books, but Dumbledore creates the impression that he didn't know that Sirius was innocent. Whether you want to believe that is up to you.

There are some arguments that at least lead to reasonable doubt.

• Sirius was sent to Azkaban without a trial, because everybody presumed he was guilty. But everybody else got a trial, even Bellatrix and her group who tortured the Longbottoms.

  the woman (Bellatrix) with the heavy-lidded eyes looked up at Crouch and called, “The Dark Lord will rise again, Crouch! Throw us into Azkaban; we will wait! He will rise again and will come for us, he will reward us beyond any of his other supporters! We alone were faithful! We alone tried to find him!”

• Snape was given a trial and was acquitted on Dumbledore's word

  “Snape has been cleared by this council,” said Crouch disdain­fully. “He has been vouched for by Albus Dumbledore.”

• They made a deal with Karkaroff to release him if he gives enough other names.

  “Crouch is going to let him out,” Moody breathed quietly to Dumbledore. “He’s done a deal with him. Took me six months to track him down, and Crouch is going to let him go if he’s got enough new names. Let’s hear his information, I say, and throw him straight back to the dementors.”

• If they believe Sirius had an important position, it makes sense to question him about other Death Eaters.
• Many other Death Eaters had the opportunity to get the charges against them released.
• Even if Dumbledore believes that Sirius worked for Voldemort, it would make sense to find out what he told him, maybe even why he did it.
• Dumbledore benefits from Sirius being in prison. Sirius is Harry's guardian. Dumbledore sends Hagrid to get Harry to the Dursleys before Sirius confronts Peter. Some would say that was his plan before he even knew Harry's parents were dead. It is essential for his plans that Sirius doesn't get Harry away from the Dursleys, and this stays true even after he knows for sure that Sirius is innocent. So it is really a happy coincidence for Dumbledore that Sirius is locked away without a trial.
• Even after Dumbledore knows that Sirius is innocent, he doesn't do anything to clear Sirius of the accusations.

---

Sirius doesn't try to get into Gryffindor to warn Harry, he does so to catch Wormtail. The portrait is just a portrait, and in his way.

Answer 2

The other answer's implicit suggestion that there is reasonable doubt that Dumbledore did not know Sirius was innocent is not quite compatible with the book. Specifically, near the end Dumbledore stated why Sirius had been imprisoned and why he now believed Sirius to be innocent:

[...] Dumbledore turned to Harry and Hermione. They both burst into speech at the same time.

[...]

But Dumbledore held up his hand to stem the flood of explanations.

"It is your turn to listen, and I beg you will not interrupt me, because there is very little time," he said quietly. "There is not a shred of proof to support Black's story, except your word -- and the word of two thirteen-year-old wizards will not convince anybody. A street full of eyewitnesses swore they saw Sirius murder Pettigrew. I myself gave evidence to the Ministry that Sirius had been the Potters' Secret-Keeper."

"Professor Lupin can tell you --" Harry said, unable to stop himself

"Professor Lupin is currently deep in the forest, unable to tell anyone anything. By the time he is human again, it will be too late, Sirius will be worse than dead. I might add that werewolves are so mistrusted by most of our kind that his support will count for very little and the fact that he and Sirius are old friends --"

"But --"

"Listen to me, Harry. It is too late, you understand me? You must see that Professor Snape's version of events is far more convincing than yours."

"He hates Sirius," Hermione said desperately. "All because of some stupid trick Sirius played on him --"

"Sirius has not acted like an innocent man. The attack on the Fat Lady -- entering Gryffindor Tower with a knife -- without Pettigrew, alive or dead, we have no chance of overturning Sirius's sentence."

"But you believe us. "

"Yes, I do," said Dumbledore quietly. "But I have no power to make other men see the truth, or to overrule the Minister of Magic...."

[...]

"What we need," said Dumbledore slowly, and his light blue eyes moved from Harry to Hermione, "is more time. "

"But --" Hermione began. And then her eyes became very round. "OH!"

"Now, pay attention," said Dumbledore, speaking very low, and very clearly. "Sirius is locked in Professor Flitwick's office on the seventh floor. Thirteenth window from the right of the West Tower. If all goes well, you will be able to save more than one innocent life tonight. But remember this, both of you: you must not be seen. Miss Granger, you know the law -- you know what is at stake... You -- must -- not -- be --seen. "

According to Dumbledore, he had believed Sirius to be guilty because he had believed him to be the secret keeper for the Potters, not knowing that they had changed it to Peter at the last minute. Earlier, Sirius himself had told Harry that he considered himself guilty for persuading the Potters to change the secret keeper:

"Harry... I as good as killed them," [Sirius] croaked. "I persuaded Lily and James to change to Peter at the last moment, persuaded them to use him as Secret-Keeper instead of me... I'm to blame, I know it... The night they died, I'd arranged to check on Peter, make sure he was still safe, but when I arrived at his hiding place, he'd gone. Yet there was no sign of a struggle. It didn't feel right. I was scared. I set out for your parents' house straight away. And when I saw their house, destroyed, and their bodies... I realized what Peter must've done... what I'd done.... "

And that is why he did not even attempt to exonerate himself when sentenced to Azkaban, because he felt guilty even though he was not. It is believable that he never told Dumbledore, for the same reason, because at that time it was not known that Voldemort survived, so there was no real need to expose Peter who had fled.

Also, it is likely that Sirius had his wand pointed at Peter when Peter cut off his thumb behind his back and then blew up the street behind him before vanishing into the sewers below. The eyewitnesses would have seen Peter gone after the explosion, and conclude that Sirius was responsible.