Why didn't Voldemort suspect Snape as a double agent during Philosopher's Stone?

Question

I read something online that got me thinking about this. Why didn't Voldemort suspect Snape had defected from the Death Eaters and was now working for Dumbledore during the events of *Philosopher's Stone?

Voldemort was possessing Quirrell's body and his head was protruding from the back of Quirrell's - in other words, Voldemort was with Quirrell constantly during the events of Philosopher's Stone, presumably overhearing whatever Quirrell himself heard.

Snape cornered Quirrell more than once (Halloween, when Quirrell let the troll in, and the night Harry broke into the Restricted Section over the Christmas holidays to look for information on Nicholas Flamel) and openly threatened him against working for Voldemort and pressuring him to declare his loyalties to Dumbledore. This obviously revealed Snape's loyalty to Dumbledore to Quirrell, and presumably Voldemort, and I can't think of a reason why Voldemort wouldn't have been able to hear Snape strong-arming Quirrell perfectly clearly.

Why didn't Voldemort attempt to make contact with Snape during Philosopher's Stone? After all, Snape was supposedly Voldemort's most faithful servant. How is it Voldemort didn't suspect Snape was working for Dumbledore and didn't orchestrate a move against him? Snape wasn't even pretending to be a double agent during Philosopher's Stone, so why Voldemort didn't kill Snape as soon as he was physically able, or have Quirrell attempt to kill him, is unclear.

So yes, why didn't Voldemort suspect Snape as a double agent during the events of Philosopher's Stone?

Answer 1

From The Half Blood Prince:(emphasis mine)

“I think you next wanted to know,” he pressed on, a little more loudly, for Bellatrix showed every sign of interrupting, “why I stood between the Dark Lord and the Sorcerer’s Stone. That is easily answered. He did not know whether he could trust me. He thought, like you, that I had turned from faithful Death Eater to Dumbledore’s stooge. He was in a pitiable condition, very weak, sharing the body of a mediocre wizard. He did not dare reveal himself to a former ally if that ally might turn him over to Dumbledore or the Ministry. I deeply regret that he did not trust me. He would have returned to power three years sooner. As it was, I saw only greedy and unworthy Quirrell attempting to steal the stone and, I admit, I did all I could to thwart him.”

Answer 2

I think it's worth answering here because the question references Voldemort's thinking during the events of Philosopher's Stone - none of the answers I see truly address the situation from that perspective so here goes:

Looking solely at the text of Book 1 - there would be no reason for Voldemort to think Snape had necessarily turned against him. Consider the scene between Snape and Quirrell in the forest:

"Oh I thought we'd keep this private", said Snape, his voice icy. "Students aren't supposed to know about the Sorcerer's Stone, after all"

Later in the exchange, he says:

"Have you found out how to get past that beast of Hagrid's yet?"

Then finally:

"You don't want me as your enemy Quirrell."

Consider this interaction from Voldemort's point of view:

Snape doesn't know Quirrell is evil, so, he (Vold) assumes that Snape considers Quirrell as legitimate and working for Dumbledore, protecting the Stone. From Voldemort's point of view, if Snape likewise were working for Dumbledore and attempting to protect the stone, why would he be accosting somebody on the same team for information about how to purloin the stone?

From this perspective, Snape is clearly evil: in fact, this is what we are supposed to think, given that we see the interaction from Harry's point of view, Harry comes away resolute in his opinion that once and for all, Snape is disloyal and evil - exactly what Voldemort would think as well, which, to him, Voldemort, is a positive situation.

Quirrell later asserts to Harry that he believed Snape was onto him:

He suspected me all along. Tried to frighten me..."

Ultimately though, had Snape, from Voldemort's perspective, truly considered Quirrell an objective danger to Dumbledore's plans for the stone, Snape would have turned to Dumbledore. Instead, Snape seems to be pursuing this on his own, which logically means Snape isn't looking out for Dumbledore's plans, but his (Snape's) own plans.

Voldemort had no reason in Book 1 to distrust Snape because Snape, as always, never revealed his ultimate loyalty.

Answer 3

Maybe Voldemort assumed that Snape was pretending to be loyal to Dumbledore. After all, the dark lord hadn't revealed himself to Snape yet, and Voldemort, being the mastermind he was, knew that a double agent would have to keep up appearances. Perhaps Voldemort thought Snape was biding his time till the Dark Lord rose once again (while also protecting the stone from another professor whom Snape assumed was attempting to steal the stone). As long as Voldemort remained hidden, he knew it was best for Snape to appear loyal to Dumbledore in anyway possible.

Answer 4

Voldemort must have thought that Snape didn't know Voldemort was inside the body of Quirrell, He just had to keep the stone safe, because he wouldn't get trusted by dumbledore.

Answer 5

Personally I think that Prof Quirrell didn't reveal to Snape that night when Snape confronted him in the hallway outside of the library in Sorceror's Stone, why he was actually looking for the stone. All we saw was that Snape was telling him not to make an enemy of Snape. Voldemort wouldn't want Quirrell to blow his cover thus loosing the element of surprise. And Voldemort would have expected Snape to keep up appearances while still being planted at Hogwarts. I've thought of this topic myself, very clever move by Rowling.