Why didn't Quirrell kill his way to the Stone?

Question

In Philosopher's Stone Quirrell goes down the trapdoor, gets through all the defences, and comes to the mirror.

I've said on answers before that I reckon the defences weren't meant to stop anyone at all, merely slow them down so Dumbledore could go take a look. Nonetheless, to get to the Stone you have to pass a giant three-headed dog, and a troll.

Quirrell took the time to figure out how to get past Fluffy, and he 'had a way with trolls': he put Fluffy asleep and knocked out the troll (with his own club, I believe the implication was) (not sure how much of a 'way' Quirrell has with trolls in this case: you hardly need to be diplomatic to knock someone unconscious).

But why? Why put Fluffy asleep? Why knock out the troll? Why not just kill them both and stroll through?

I don't think it's because the creatures cannot be killed by magical means. There are a ton of spells that can kill, and many use 'natural' power (incendio causes fire, as opposed to avada kedavra, I mean).

What were Quirrell and Voldemort's motives for not killing Fluffy and the troll?

Answer 1

A potential answer can be found on page 289 in the hardback book when Quirrell explains to Harry that

"Certainly, I have a special gift with trolls - you must have seen what I did to the one in the chamber back there? Unfortunately, while everyone else was running around looking for it, Snape, who had already suspected me, went straight to the third floor to head me off - and not only did my troll fail to beat you to death, that three-headed dog didn't even manage to bite Snape's leg off properly."

Quirrell's statements about Fluffy not biting Snape properly and his troll not beating Harry et al to death suggests that Quirrell deliberately thought to use Fluffy and the troll against Snape and Harry should they try and foil his plan.

He considers his handling of trolls as a 'special gift' and he had to ply Hagrid for very specific information on Fluffy. Combined with the above suggestion - re: using challenges on those who would pursue him, Quirrell was confident that only he and Voldemort would be able to get past the challenges.

If he/they can get past but still allow for these challenges to pose a potentially lethal challenge for those in pursuit like Snape or Harry and company, then why not?

Answer 2

This isn't a canon based answer, but I would assume it was in order to keep his cover.

Quirrell had remained at Hogwarts all year, and still his secret hadn't been discovered. Snape suspected, but if he had been able to prove what Quirrell was up to then there would be no way he'd have remained at the school to teach DADA. Clearly Quirrell was planning on keeping his true intentions a secret for as long as was required.

His first attempt (as far as we know) to get to the Philosopher's Stone was Halloween, and Harry & co. catch him trying to get it close to the end of the year. That is a long time to go without even attempting to get the stone. Considering that he got the information on how to tame Fluffy months before when he gave Hagrid the dragon egg, he had the knowledge of getting past at least the first defense of the stone.

I don't think that Quirrell would have waited that long for a second attempt. There would likely have been other times that Dumbledore was called away on urgent business etc. that would have allowed him to sneak past Fluffy and attempt a couple of the trials. He had no way of knowing how many there were, or how long they would take him, so could not go in all guns blazing. If he had been discovered he would lose the chance to get at the stone for good.

Therefore in order to be able to go down the trapdoor numerous times, he needed to leave as little trace of his presence as possible. He likely cleaned up after himself whenever he entered and left. The only reason the troll was unconscious at the time Harry went down would have been because Quirrell was already there.

Answer 3

A few reasons spring to mind:

1. He doesn’t want to attract unwanted attention.

   Killing a troll or three-headed dog is possible, but it probably isn’t easy. Such a creature is liable to make a lot of noise if, for example, you try to burn it alive.

   The third-floor corridor isn’t so far from parts of the castle frequented by students, and we know that teachers and prefects patrol the corridors at night. There’s a high risk of somebody hearing him trying to subdue the creature, and being caught in the attempt.

   It’s also possible that Dumbledore can detect unusually dark magic inside the school (such as Avada Kedavra). Those are not spells usually cast inside a school; they’d be bound to attract attention if noticed.

2. He doesn’t want to leave a trace of failed attempts.

   If Quirrell finds an unexpected defence – for example, a magical mirror hiding the stone – he wants to be able to leave without anybody realising he was there. If Dumbledore realises that somebody was there, he’s bound to increase the defences around the stone, which makes Quirrell’s job harder. The stone might even be moved to an entirely different location.

   He leaves the harp in Fluffy’s chamber – he can pick it up on the way out – and I’m sure the troll won’t have any lasting damage from being knocked out. Neither are going to tell Dumbledore about Quirrell; they lack the intelligence and language skills to do so.

Answer 4

It let them have multiple tries, and a chance to steal it undetected.

If Fluffy was killed or injured, it would make it obvious that someone was trying to get to the Philosopher’s Stone. Harry, Ron, and Hermione used Fluffy to figure out if the Stone was still safe and protected - Dumbledore and the rest of the staff could do the same.

“Every time they passed the third-floor corridor, Harry, Ron and Hermione would press their ears to the door to check that Fluffy was still growling inside. Snape was sweeping about in his usual bad temper, which surely meant that the Stone was still safe.”
_{^{- Harry Potter and the Philosopher's Stone, Chapter 14, (Norbert the Norwegian Ridgeback)}}

This wouldn’t be as much of a problem if they successfully stole the Stone, but if they got only part of the way through and then failed to get it, they’d cause Dumbledore to increase the protection. After the break-in at Gringotts, Dumbledore moved the Stone to Hogwarts, and after the failed attempt at Hallowe’en, he added the Mirror of Erised to the Stone’s protection. Continued failed attempts would just make him keep increasing its protection, making it harder to steal it. It’d still be useful if Quirrell and the Dark Lord were able to steal the Stone successfully, since the Hogwarts staff would remain unaware of its absence or the Dark Lord’s return.

In addition, killing Fluffy and the troll might not be that easy.

The Dark Lord was still weak, and Quirrell was being weakened by the Dark Lord possessing him - it might not even have been possible for them to kill Fluffy and the troll in the state they were in. We don’t know much about three-headed dogs, but Hagrid seemed to think taking care of one would be comparable to taking care of a dragon, so they’re probably fairly difficult to handle.

“So I told him, after Fluffy, a dragon would be easy …”
_{^{- Harry Potter and the Philosopher's Stone, Chapter 16, (Through the Trapdoor)}}

Trolls are known to be very strong, very violent, and large.

“The troll is a fearsome creature up to twelve feet tall and weighing over a tonne. Notable for its equally prodigious strength and stupidity, the troll is often violent and unpredictable.”
_{^{- Fantastic Beasts and Where to Find Them}}

Even if it wasn’t a bad strategy to attempt to kill the creatures guarding the Stone, it’s not clear that Quirrell and the Dark Lord would actually be able to successfully kill both of the creatures in their way to the path of the Stone. Neither of them was at their strongest, and magical creatures can be quite difficult to handle, especially as they can be resistant to spells.