Did Lord Voldemort not know that Snape was an accomplished Occlumens?

Question

Severus Snape gives a detailed explanation to each of Bellatrix Lestrange's accusations in Harry Potter and the Half-Blood Prince.

From what he says, I cannot help wondering if he ever used Occlumency against Lord Voldemort.

As well, is it not equally likely that he could have used the same against Dumbledore? In the book Half-Blood Prince, it is evident that Dumbledore did know of Snape's ability to use Occlumency (judging from the fact Dumbledore asked Snape to teach Occlumency to Harry), and, by his nature, had nothing but "trust" alone to believe in Snape's loyalty.

Yet, why is Lord Voldemort unsuspecting in this matter?

Answer 1

As E.T. said, Voldemort does not trust and leaves nothing to chance, but there are other reasons he had for believing that Snape was incapable of hiding information from him.

First, there are two branches of mind-manipulation in the Potterverse. The first is Occlumency and the second is Legilimency. Occlumency is purely defensive. Snape tells Harry in OotP chapter 24:

"Occlumency, Potter. The magical defense of the mind against external penetration. An obscure branch of magic, but a highly useful one."

Later in the same chapter, Snape and Harry have another conversation:

Snape looked back at him for a moment and then said contempuously, "Surely even you could have worked that out by now, Potter. The Dark Lord is highly skilled in Legilimency--" "What's that? Sir?" "It is the ability to extract feelings and memories from another person's mind--"

There are several reasons Voldemort would have known about Snape's abilities as an Occlumens:

1. Voldemort knew he, personally, was a skilled Legilimens. He used the ability frequently to determine if those around him were lying to him, he used Legilimency and his connection to Harry to delve into Harry's mind and manipulate him, and it was probably unfathomable to him that anyone could be more skilled at Occlumency than he was at Legilimency.
2. According to this timeline of Severus Snape at the Harry Potter Lexicon, Snape joined the Deatheaters when he was roughly 18/19 years old. Thus, if I interpret it correctly, he was a Deatheater before he was a member of the Order of the Phoenix. Voldemort knew the strengths and weaknesses of his followers--especially those Deatheaters who were higher up in the organization. Having an Occlumens at your disposal had the potential to be very useful, and while Voldemort himself could practice Legilimency, there is nothing to suggest that being skilled in one necessarily meant you were also skilled in the other. Had Snape joined the Deatheaters after aligning himself with the OotP, or if he'd still had serious ties to the Order or Hogwarts when he joined, I would agree that he might have tried to keep the secret, but at the time he really had nothing to hide.
3. It would have been more dangerous for Snape to attempt to conceal his Occlumency from Voldemort than it would be for him to be up-front about it. Keeping such a skill secret from the Dark Lord would have appeared to be nothing less than treacherous, and we know what Voldemort did to followers whose loyalty appeared to waver.

Answer 2

I'm pretty sure I have the definitive answer:

1. Voldemort was arrogant. He would believe that no one was more powerful than him. Therefore he would have thought he was a more powerful Legilimens than anyone was Occlumens.

   So, for example, in DH when Snape comes to the meeting with his information about Harry's time of leaving the Dursleys (information he himself planted) Voldemort obviously used Legilimens on Snape. Snape purposefully never avoids Voldemort's eyes, openly allowing Voldemort access to his mind.

   Clearly Snape felt that he could hide everything from Voldemort. More interesting is that Snape must have altered his memory very well because Voldemort would need to 'see' Snape's memory of learning from Mundungus when and where Harry was leaving, while hiding the part of the memory of being the one to suggest there be seven Harry's. Voldemort would never have suspected that anyone could be more powerful than him.

2. As for Dumbledore not using Legilimens on Snape, it simply comes to this: unlike Voldemort, Dumbledore knew the power of love. When Snape came to Dumbledore asking for protection for Lily, that was evidence that Snape loved Lily.

   When she was murdered and Snape was broken apart it was clear that his love was real. Dumbledore could recognize that. He knew from personal experience the power that remorse has.

   No, Dumbledore didn't need to use spells to see that Snape regretted what he did and knew, just as he knew that Harry would never stop hunting Voldemort because he murdered his parents, that Snape would do whatever it took to protect Lily's son and get revenge against Voldemort.

   Snape worshipped Voldemort until he threatened the woman he loved which drove him into the arms of his biggest rival.

Answer 3

I believe Voldemort did know Snape was an accomplished Occlumense.

I think Voldemort was versed in the art as well.

Voldemort doesn't trust. It's just not something he does. I think he must have used it against all his followers, or at least the ones he "trusted" with more sensitive data/missions.

Answer 4

Voldemort would have known; I agree, why would Snape hide such a useful skill prior to his joining the Order? And even afterwards....surely Voldemort knew he had this ability and that it was useful for Snape in spying on Dumbledore?

Don't forget, V wants Snape at the school B/C he thinks he needs a spy there. That's the only reason he doesn't send Snape into direct combat, or reconnaissance missions, or whatever other kind of work V might need at any moment. And why in 5, he doesn't have Snape sent to try to get the prophecy or have anything to do with the Ministry battle.

Being at the school is a good situation for Snape as well, because he doesn't have to kill or torture or do anything that might be morally compromising. So he would probably want to stay there.