Science Fiction & Fantasy Stack Exchange is a question and answer site for science fiction and fantasy enthusiasts. It only takes a minute to sign up.
Sign up to join this community
When Voldemort planned to kill baby Harry, Snape leaked this to Dumbledore, who in turn alerted the Potters, which finally cost Voldemort his body. If the Potters didn't know beforehand, he would have had an element of surprise, or he could have sneakily killed Harry.
Voldemort definitely knew that Snape leaked the information because Pettigrew was his inside man.
Why did he then trust a traitor after his return?
There is no evidence to show that Voldemort ever knew Snape had betrayed him by revealing his plans to Dumbledore; on the contrary, there is a fair amount of circumstantial evidence to indicate that he didn’t. For one thing, if he had known, Snape would almost certainly have died before Philosopher’s Stone even begins, and all seven books would have been very different.
Voldemort definitely knew that Snape leaked the information because Pettigrew was his insider man.
Your logic does not really hold water here.
As QuestionAuthority’s answer says, Voldemort knew that Dumbledore had heard the entire prophecy—and thus knew more than Snape was able to tell Voldemort. He also knew, through Pettigrew, that the Potters were hidden under a Fidelius Charm. But that was all he knew.
It so happens that the Fidelius Charm probably came about mainly because Snape told Dumbledore that Voldemort had interpreted the prophecy to refer to the Potters, not the Longbottoms—but how would Voldemort have known about this? There are only really two ways Voldemort could have found out: from his spy Pettigrew, or from Snape himself.
That Snape didn’t volunteer the information to Voldemort himself does not need much by way of convincing argumentation. He would know that doing so would be signing his own death warrant. No need to even entertain the notion.
And Pettigrew almost certainly couldn’t have told Voldemort, because there’s no reason to believe he ever knew. As soon as Dumbledore found out about the Potters being targeted, he used Snape’s feelings for Lily to make him turn spy against Voldemort, which was a very valuable asset to him. He would obviously not do anything to jeopardise it if he could help it, and telling anyone—even those closest to him—would be doing just that. So he almost certainly never told anyone else that Snape was now a spy for him, including Pettigrew, and Pettigrew never knew.
Pettigrew knew that Dumbledore wanted the Potters protected, and he might even have suspected that this was based on spy intel that Dumbledore had received about Voldemort’s plans. But the only way he could have known that the intel came from Snape would be if Dumbledore had told him (or if Snape had, but the point two paragraphs up holds true here as well), which would have been a very unwise and un-Dumbledorish thing to do.
Voldemort in turn knew the first half of the prophecy from Snape. He knew from his own knowledge of the wizarding world and his spies (presumably) that the prophecy could refer to either the Potters or the Longbottoms, and he knew from Snape that Dumbledore knew this too (if not more). He also knew from Pettigrew that the Potters had been Fideliussed away on Dumbledore’s orders.
He could not know, however, why Dumbledore had chosen to protect the Potters, nor whether he had taken (or was taking) steps towards protecting the Longbottoms in a similar manner. He also did not know whether the final part of the prophecy had made it clear that it did indeed refer to the Potters and not the Longbottoms, so that only the Potters needed protection. All he knew was that he selected the most likely family, and this family was protected by Dumbledore.
He was clever enough to know that Dumbledore had spies within Death Eater ranks just as Voldemort himself had spies within Phoenix ranks. Even if he did ever suspect that Dumbledore’s decision to protect the Potters was borne out of spy intel, rather than simply based on the information he himself already had available to him, there is nothing that would indicate that Snape in particular was the source of that information.
Pettigrew was the Dark Lord’s spy in the Order of the Phoenix, but Dumbledore didn’t tell them the whole truth when it was better that things be kept as quiet as possible. We know that Dumbledore avoided telling Harry that Snape was the one who’d heard the prophecy - Harry only found out because he heard about it from Trelawney, who didn’t even know she made a prophecy. The Order didn’t know that it was Snape either - they only found out when Harry told them.
“I’d love to know what Snape told him to convince him,’ said Tonks.
‘I know,’ said Harry, and they all turned to stare at him. ‘Snape passed Voldemort the information that made Voldemort hunt down my mum and dad. Then Snape told Dumbledore he hadn’t realised what he was doing, he was really sorry he’d done it, sorry that they were dead.’
‘And Dumbledore believed that?’ said Lupin incredulously. ‘Dumbledore believed Snape was sorry James was dead? Snape hated James …”
- Harry Potter and the Half-Blood Prince, Chapter 29 (The Phoenix Lament)
Dumbledore didn’t tell the Order, so Pettigrew wouldn’t have found out as a spy that Snape was the one who told Dumbledore of the prophecy. Therefore, Pettigrew couldn’t tell the Dark Lord, and it’s unlikely that the Dark Lord would have found out Snape was responsible for it in any other way.
We know that Snape told the Dark Lord everything he heard of the prophecy. Presumably, that would include that it was made in front of Dumbledore, meaning the Dark Lord would know that Dumbledore would have heard the prophecy himself.
“The – the prophecy … the prediction … Trelawney …’
‘Ah, yes,’ said Dumbledore. ‘How much did you relay to Lord Voldemort?’
‘Everything – everything I heard!’ said Snape. ‘That is why – it is for that reason – he thinks it means Lily Evans!”
- Harry Potter and the Deathly Hallows, Chapter 33 (The Prince’s Tale)
The part the Dark Lord heard, and would have known Dumbledore heard, said that the boy who could defeat him would be born in July to parents who defied him three times. From that, he was easily able to figure out the two boys who fit the prophecy, and likely wouldn’t be surprised that Dumbledore could have reasoned out who they were and taken measures to protect them.
“My – our – one stroke of good fortune was that the eavesdropper was detected only a short way into the prophecy and thrown from the building.’
‘So he only heard –?’
‘He heard only the beginning, the part foretelling the birth of a boy in July to parents who had thrice defied Voldemort.”
- Harry Potter and the Order of the Phoenix, Chapter 37 (The Lost Prophecy)
That the Potters were protected wouldn’t be particularly surprising or unexpected to the Dark Lord, knowing Dumbledore had heard the prophecy, so he’d have no reason to believe that their protection was the result of Snape telling Dumbledore rather than Dumbledore’s own reasoning.
Dumbledore heard the full prophecy from Trelawney. He also knew that Snape heard a part of the prophecy and was caught by his brother Aberforth. This part was
The one with the power to vanquish the Dark Lord approaches.
Born to those who have thrice defied him, born as the seventh month dies.
It is no stretch of the imagination that Dumbledore immediately realized that Voldemort would try to eliminate this perceived danger. As the prophecy was told before Harry and Neville were born, Dumbledore didn't immediately know who this vanquisher was going to be, but after they were born it became clear. So protecting the Potters has nothing to do with Snape leaking information.
Voldemort in turn knew that Dumbledore heard the prophecy in person, because Snape told him. So there is no reason to suspect Snape because Dumbledore wanted the Potters (and Longbottoms) protected.
Voldemort didn't know Snape was the trator
No one really knew Snape had leaked the secrets to Dumbledore. Here, Bellatrix lists why she does not trust Snape:
"Narcissa, I think we ought to hear what Bellatrix is bursting to say; it will save tedious interruptions. Well, continue, Bellatrix," said Snape. "Why is it that you do not trust me?"
"A hundred reasons!" she said loudly, striding out from behind the sofa to slam her glass upon the table. "Where to start! Where were you when the Dark Lord fell? Why did you never make any attempt to find him when he vanished? What have you been doing all these years that you've lived in Dumbledore's pocket? Why did you stop the Dark Lord procuring the Sorcerer's Stone? Why did you not return at once when the Dark Lord was reborn? Where were you a few weeks ago when we battled to retrieve the prophecy for the Dark Lord? And why, Snape, is Harry Potter still alive, when you have had him at your mercy for five years?"
None of these questions were "Why did you leak secrets to Dumbledore?" If Voldemort didn't tell Bellatrix, his most trusted advisor, there is a large chance he didn't know. For a full account of Snape's answers to Bellatrix, see Hogwarts is Here.
