Given that there is a hole drilled through hogwarts, should it now be possible for everyone to deduce that Harry and Quirrell have a telepathic resonance? (Quirrell and Hermione has less plausible priors, plus Quirrell would have arrived earlier in that case).
Eventually this may allow someone to deduce that he is Voldemort, but even before that, some characters should notice that they are confused.
Given that there is a hole drilled through hogwarts, should it now be possible for everyone to deduce that Harry and Quirrell have a telepathic resonance?
I don’t think so. Jumping from ‘Quirrel knows where to go’ to ‘telepathic resonance’ seems like a major example of privileging the hypothesis.
Even ignoring the issue that as far as we know from canon & MoR, “telepathic resonance” is a completely unknown and novel phenomenon and that people cannot know Quirrel is homing in on Harry rather than say Hermione or the troll, there are still dozens of more likely explanations: the school wards; troll tracking skills as part of the Defense professor’s esoteric & eldritch lore; spy devices planted throughout the school; an Eye (“constant vigilance!”) or other snooping devices; the Marauder’s Map; supernaturally good hearing; tracking charms placed on Harry (IIRC, didn’t Quirrel already do just that with Draco?); information from the future (if notes can be passed about bullies, why not trolls?); ghost/poltergeist/painting messages; etc.
From the POV of Dumbledore, there are several unexplained things about Quirrel’s behavior:
Quirrel not only homed in on the troll. At some point he suddenly became so frantic that he blasted his way through Hogwarts. (He didn’t do so immediately; indeed when the he goes to look for the troll with the rest of the Professors, he exhibits nothing like this kind of urgency.) This happened just as Harry encountered the troll.
Then, without having reached the troll, he suddenly stopped and said there was no more need to rush. Just as Harry killed the troll and Dumbledore arrived to secure the scene.
All the explanations that say he was tracking the troll and not Harry, imply he should have reached the troll before Harry did. After all, he left before Harry, he was probably moving faster (two-person broomstick vs. three-person), and he was moving in a straight line, blowing holes through the castle. Instead, he didn’t even arrive by the time Dumbledore did.
Now let’s consider your suggestions: I think some are plausible but most are not.
the school wards;
Dumbledore would know everything the wards reported. If they alerted Quirrell to the location of the troll, why not Dumbledore (or McGonnagal)? And when they reported the death of Hermione, this should have caused Quirrell to hurry more, not to proclaim there was no more danger.
troll tracking skills as part of the Defense professor’s esoteric & eldritch lore
Then why didn’t he find the troll before Harry did? (See above)
spy devices planted throughout the school
Moderately plausible. But: spy devices which are better than the Hogwarts wards? Or, which allow him to remotely look at any area instead of merely being alerted when a condition is triggered? I don’t think Dumbledore approve of him taking such power. And Dumbledore would of course check his story—so the spy devices would need to actually exist, and not have been detected.
Eye (“constant vigilance!”) or other snooping devices; [...] supernaturally good hearing;
Not foreshadowed, hence bad storytelling.
the Marauder’s Map;
Then why hadn’t he consulted it right away before the professors left to hunt the troll, and see Hermione was out there?
It suspends disbelief that Quirrel wouldn’t do so—without a particular reason, but just because he forgot—and then apparently two minutes later he would remember to do so, and so find Harry.
And if he was following the map, why did he declare that “The crisis is over”? I don’t know if the troll would show up on the map, but regardless, even though he saw Dumbledore appear, he also saw Hermione disappear. Surely he wasn’t so optimistic as to assume that disappearance (alone) was something other than death.
Also, what plausible excuse could he present for having the Map while the Twins are Obliviated? Dumbledore is the one main character who definitely knows of the Map, so Quirrel would want to hide it from him.
tracking charms placed on Harry (IIRC, didn’t Quirrel already do just that with Draco?);
Then, against, how did he know when “The crisis is over” and he could stop hurrying towards Harry?
information from the future (if notes can be passed about bullies, why not trolls?);
With future intel, why hadn’t he prevented the disaster entirely? Why hadn’t he warned anyone? Why had he still gone out to search for the troll, in such a hurry that he burned through walls to get to it, if he knew he wouldn’t make it in time? Why didn’t he share the future intel with the other professors hunting the troll? That doesn’t sound like a time-loop.
ghost/poltergeist/painting messages;
Possible (although can paintings or ghosts move quickly enough to deliver the message in time?) but again, why did he stop?
From the POV of Dumbledore, there are several unexplained things about Quirrel’s behavior
Most of those can be explained away with reference to the others and the poor information available to Dumbledore. What stops Quirrel from saying he blasted off when he detected Hermione had been trapped on the terrace and the troll was immune to sunlight? There are no atomic clocks here. Similarly, if he had some surveillance system, he can say he stopped when Hermione died and there was no more need to hurry (alas); between the wards and the soulsplosion, there’s plenty of ways for someone like Quirrel to plausibly get the info without positing bizarre unique psychic bonds.
Dumbledore would know everything the wards reported. If they alerted Quirrell to the location of the troll, why not Dumbledore (or McGonnagal)?
There are multiple levels to the wards, and we don’t know what Dumbledore or McGonagal do or do not know—I’ve pointed out that Dumbledore wasn’t even in the castle, it seems, and McGonagal has no access to phoenixes and is not a battle mage who can burn through ancient magical walls at the speed of flight.
Then why didn’t he find the troll before Harry did? (See above)
Perhaps he was bored, or piqued at the distrust.
Moderately plausible. But: spy devices which are better than the Hogwarts wards? Or, which allow him to remotely look at any area instead of merely being alerted when a condition is triggered? I don’t think Dumbledore approve of him taking such power. And Dumbledore would of course check his story—so the spy devices would need to actually exist, and not have been detected.
We know he admires and imitates Muggle technology—recall the very first class. A spy network is perfectly reasonable. Of course Dumbledore would disapprove and would check for its existence, but sacrificing a spy network seems like a small price to not be the culprit for murdering a little girl. He can always replace it or put in a different system.
Not foreshadowed, hence bad storytelling.
I’m afraid out-of-universe reasoning is not really available to the characters. :)
Then why hadn’t he consulted it right away before the professors left to hunt the troll, and see Hermione was out there?
He can claim she was nowhere near and it was not an emergency until she was trapped on the terrace and it became clear that something had gone terribly wrong.
Also, what plausible excuse could he present for having the Map while the Twins are Obliviated? Dumbledore is the one main character who definitely knows of the Map, so Quirrel would want to hide it from him.
For all we know, Dumbledore might have a hand in the Obliviation. And did Quirrel expect the Obliviation to be detected? One suspects not: he wasn’t expecting Harry to be there either.
Then, against, how did he know when “The crisis is over” and he could stop hurrying towards Harry?
Already explained.
With future intel, why hadn’t he prevented the disaster entirely? Why hadn’t he warned anyone?
“I could explain, but I fear the necessary graphs would make your head explode and neither Snape nor Dumbledore could follow my exact reasoning. As Mr Potter might say, ‘do not mess with time’.”
Possible (although can paintings or ghosts move quickly enough to deliver the message in time?) but again, why did he stop?
Him stopping is really not as hard as you think it is.
Again, consider the alternatives here. That he has a unique, unprecedented, unnamed, inexplicable, unknown-to-all-but-him-and-Potter (AFAIK) telepathic bond and also in conjunction with an elaborate theory about him trying to kill Hermione (why?) this explains some movements during a chaotic 2 minutes or less of troll-hunting based on finely-parsed counterfactuals of what he would and would not know where you suppose that characters would place high confidence in their deductions about an infamously devious, whimsical, highly-knowledgeable intelligent weirdo.
The triggers you propose wouldn’t work, assuming that Dumbledore should be able to make a good estimate of Quirrell’s speed and the time he spent traveling. I also think that Dumbledore should have noticed when Quirrell stopped, since by then he had already returned to Hogwarts.
Fred and George spent quite a long time fighting the troll; if Quirrell had started his mad dash when the troll reached the terrace, when Hermione had her legs bitten off, or when Harry, Fred, and George reached the scene, he would have arrived before the end of the fight. I guess, theoretically, his vast, previously-undetected spy network could have noticed the battle at exactly the right time, but that seems implausible to me, and it would seem similarly implausible to Dumbledore. Quirrell could also have been triggered by Hermione’s death, but I suspect Dumbledore could falsify that one; if he had started when Hermione died, he wouldn’t have been able to cut such a huge swath of destruction through Hogwarts in the time between Hermione’s death and his stopping.
It’s possible he was triggered by the troll’s death, but that would make no sense; as far as he should know, the end of the troll means the end of the catastrophe. I suspect Dumbledore’s first guess should be that Quirrell had put a ward on Harry (despite Dumbledore’s orders otherwise) and he was therefore able to detect when Harry started to fight… however, if Dumbledore were to actually ask Harry about this, Harry would of course tell him that, no, Quirrell isn’t able to cast any magic on him, which would probably be enough of a hint to lead Dumbledore to the correct answer.
It’s hypothesized both in canon and in Methods that Harry and Voldemort might have a connection of some sort. So, it wouldn’t exactly be unexpected and inexplicable; indeed, it seems like it’s something that Dumbledore and McGonagall might rate as high-probability conditional on Quirrelmort theory. (And I can’t imagine that psychic bonds are unheard of in Methods-world.)
assuming that Dumbledore should be able to make a good estimate of Quirrell’s speed and the time he spent traveling. I also think that Dumbledore should have noticed when Quirrell stopped, since by then he had already returned to Hogwarts.
How would he? He was not with Quirrel nor was he presumably examining the Map (if he had it).
Fred and George spent quite a long time fighting the troll
Not really? They spent maybe 30 seconds at the outside—it doesn’t take long to cast a bunch of spells and swing a sword once. In the real world, fights do not last very long. Only in movies do fights go on for entire minutes.
however, if Dumbledore were to actually ask Harry about this, Harry would of course tell him that, no, Quirrell isn’t able to cast any magic on him, which would probably be enough of a hint to lead Dumbledore to the correct answer.
Dumbledore would have to ask, though, and why would he when he would expect Harry to be ignorant? I would also note Quirrel’s own explanation to Harry about a ‘cursed artifact’, which is a likely and also fully general explanation which Dumbledore could not compel a peer of his to explain his secrets, not in a culture like Magical Britain.
It’s hypothesized both in canon and in Methods that Harry and Voldemort might have a connection of some sort.
Based largely on the events at the end of Stone, which never happened in MoR; in MoR, the only basis for this speculation is Harry being a Parseltongue. A passed on ability doesn’t suggest a live physic link.
it seems like it’s something that Dumbledore and McGonagall might rate as high-probability conditional on Quirrelmort theory.
Do they? Everyone seems quite satisfied with the David Monroe theory.
(And I can’t imagine that psychic bonds are unheard of in Methods-world.)
Ok, you’re right, there isn’t enough information to get past the prior implausibility of the hypothesis. I think the other characters should assume he placed tracking charms on Harry. Any explanation about tracking the troll or Hermione would result in him arriving earlier, and when questioned, the divination professor can say approximately when Quirrell started to move, which cross-referenced with Harry’s recollections shows that Quirrell’s actions correlate with Harry being in danger, not Hermione.
However, I assume that these tracking spells can be detected, in which case, if another character attempts to detect these spells and finds none on either Harry or Hermione, the Quirrell has done something seemingly impossible. Given this, Quirrell should probably cast such a spell on Harry before this occurs to anyone.
The problem is that Quirrell can’t cast any spells on Harry. And, furthermore, Quirrell really doesn’t want Dumbledore to find this out—Dumbledore already knows of a certain other person with an unexpected inability to cast spells on Harry Potter, and I think the hint would probably be enough for him to put the two together.
Oh, good point, I had forgot about that. In which case… Dumbledore may not be able to guess the telepathic link due to prior implausibility, but he should realize that there is something odd going on, if it crosses his mind to investigate how Quirrell knew where to go.
Of course, this may not occur for a while if at all, as Dumbledore has plenty of other things to worry about, and the obvious suspect from his POV is Lord Malfoy.
I’ve tried to make it work as a Lord Malfoy assassination, but I can’t seem to make the pieces fit together, and I don’t think Dumbledore would be able to either… Of course, it would be an easy frame-job, should Dumbledore or anyone else be interested in that. I’m going to explain why, not to convince you, but to establish why Dumbledore probably won’t accept that so readily.
First, if it were Lord Malfoy, the assassination would doubtless be for honor, which means that it should be recognizably the work of the Malfoy family. That means death via snakebite. Such an obvious killing may affect Harry’s debt, or create a new blood debt in Harry’s favor, but as has already been demonstrated Lucius doesn’t care about that very much. A mountain troll… doesn’t really have very much to do with Lucius Malfoy. It doesn’t fit the pattern.
Second, the Marauder’s Map Confunding doesn’t make very much sense. Lucius could do a lot with an Imperiused professor, but indiscriminate Legilimency doesn’t seem like one of those things. So, he shouldn’t know about the Map, and definitely shouldn’t have erased it from Fred and George’s minds. That’s not necessarily a disqualifier, but it does mean that Lucius would have to be working with either Snape or Quirrell; I’ll talk about Snape later, but if Quirrell was involved we may as well consider it a Quirrell plot, even if he collected payment from Lucius on the side.
Third, it seems unlikely that Snape is involved. Dumbledore is not opposed to him pretending to be on Lucius’s side. Indeed, Lucius Malfoy trying to pull an assassination from under Dumbledore’s nose would act sufficiently in Dumbledore’s political favor that he might be inclined to let it play out, so long as he would be able to save Hermione at the last minute. This probably wouldn’t even cost Snape much—of course an assassination in Dumbledore’s own castle would be a long shot for Lucius. However, Snape didn’t tip Dumbledore off at all. Even if he suddenly hates Dumbledore, this wouldn’t make any sense for him.
Fourth, and finally, Lucius would have to somehow find a way to circumvent the Hogwarts wards. The dementor in the Humanism arc needed a special pass from Dumbledore in order to get through the wards. Since the mountain troll is the third most perfect killing machine, after the dementor, it’s not unreasonable to suspect that it would also require a special pass from the wards. This would be a problem for Lucius Malfoy and his cronies, even with the aid of Severus Snape or another Imperiused professor. For our benefit, this points the finger squarely at Quirrell, and his secret knowledge inherited from Salazar Slytherin who made those wards; it should merely baffle poor Albus, however.
Firstly, I’m pretty sure Quirrell did it, because (a) he did it in canon and (b) we know he’s voldemort and he’s trying to turn Harry dark (c) he tried to persuade Hermione to leave. But Dumbledore knows none of this, with the possible exception of (c).
First, if it were Lord Malfoy, the assassination would doubtless be for honor, which means that it should be recognizably the work of the Malfoy family. That means death via snakebite. Such an obvious killing may affect Harry’s debt, or create a new blood debt in Harry’s favor, but as has already been demonstrated Lucius doesn’t care about that very much. A mountain troll… doesn’t really have very much to do with Lucius Malfoy. It doesn’t fit the pattern.
Lord Malfoy does not hold absolute power, and even if he could avoid punishment for murder, it would cost him political capital, he would lose swing votes and so forth. But he is not stupid, and so might kill in an uncharacteristic way because it is uncharacteristic. Yes he would want some people to recognize his revenge, but some of the wiser wizards would realize it was him anyway, and he could privately confess it to intimidate his enemies while publicly denying it to minimize the fallout.
Second, the Marauder’s Map Confunding doesn’t make very much sense. Lucius could do a lot with an Imperiused professor, but indiscriminate Legilimency doesn’t seem like one of those things.
I think Fred and George are old enough to leave hogwarts and visit the nearby village, in which case they could have been ambushed there. Do we actually know whether Imperitused people can perform memory charms? He could also have got one of his allies to do this, either a teacher or one of the older students, although this would be more risky.
Fourth, and finally, Lucius would have to somehow find a way to circumvent the Hogwarts wards.
I’m not sure how the wards work, nor who has permission to alter them. There is at least one charm that affects only dementors, so its possible that the wards might be able to detect dementors but not trolls, but that’s just conjecture.
Finally, if there is no way this could have been organized by anyone but a Hogwarts professor, then the finger of blame points squarely at Quirrell, and I think Quirrell is smart enough to avoid that (e.g. if magical creatures cannot be sneaked past the wards, why not smuggle in a lion and cast spells on it to stop magic affecting it?).
Therefore, when Dumbledore looks at the evidence there is going to be sufficient doubt over who did it, and also the secrets of Salazar Slytherin will not be implicated. If Quirrell can devise a plan to break Belltrix out of prison, he can murder a girl without getting caught.
Not to say that Harry won’t realize it was him eventually, but only after more evidence, a lot of deduction and only a few chapters from the stories’ end :)
Given that there is a hole drilled through hogwarts, should it now be possible for everyone to deduce that Harry and Quirrell have a telepathic resonance? (Quirrell and Hermione has less plausible priors, plus Quirrell would have arrived earlier in that case). Eventually this may allow someone to deduce that he is Voldemort, but even before that, some characters should notice that they are confused.
I don’t think so. Jumping from ‘Quirrel knows where to go’ to ‘telepathic resonance’ seems like a major example of privileging the hypothesis.
Even ignoring the issue that as far as we know from canon & MoR, “telepathic resonance” is a completely unknown and novel phenomenon and that people cannot know Quirrel is homing in on Harry rather than say Hermione or the troll, there are still dozens of more likely explanations: the school wards; troll tracking skills as part of the Defense professor’s esoteric & eldritch lore; spy devices planted throughout the school; an Eye (“constant vigilance!”) or other snooping devices; the Marauder’s Map; supernaturally good hearing; tracking charms placed on Harry (IIRC, didn’t Quirrel already do just that with Draco?); information from the future (if notes can be passed about bullies, why not trolls?); ghost/poltergeist/painting messages; etc.
From the POV of Dumbledore, there are several unexplained things about Quirrel’s behavior:
Quirrel not only homed in on the troll. At some point he suddenly became so frantic that he blasted his way through Hogwarts. (He didn’t do so immediately; indeed when the he goes to look for the troll with the rest of the Professors, he exhibits nothing like this kind of urgency.) This happened just as Harry encountered the troll.
Then, without having reached the troll, he suddenly stopped and said there was no more need to rush. Just as Harry killed the troll and Dumbledore arrived to secure the scene.
All the explanations that say he was tracking the troll and not Harry, imply he should have reached the troll before Harry did. After all, he left before Harry, he was probably moving faster (two-person broomstick vs. three-person), and he was moving in a straight line, blowing holes through the castle. Instead, he didn’t even arrive by the time Dumbledore did.
Now let’s consider your suggestions: I think some are plausible but most are not.
Dumbledore would know everything the wards reported. If they alerted Quirrell to the location of the troll, why not Dumbledore (or McGonnagal)? And when they reported the death of Hermione, this should have caused Quirrell to hurry more, not to proclaim there was no more danger.
Then why didn’t he find the troll before Harry did? (See above)
Moderately plausible. But: spy devices which are better than the Hogwarts wards? Or, which allow him to remotely look at any area instead of merely being alerted when a condition is triggered? I don’t think Dumbledore approve of him taking such power. And Dumbledore would of course check his story—so the spy devices would need to actually exist, and not have been detected.
Not foreshadowed, hence bad storytelling.
Then why hadn’t he consulted it right away before the professors left to hunt the troll, and see Hermione was out there?
It suspends disbelief that Quirrel wouldn’t do so—without a particular reason, but just because he forgot—and then apparently two minutes later he would remember to do so, and so find Harry.
And if he was following the map, why did he declare that “The crisis is over”? I don’t know if the troll would show up on the map, but regardless, even though he saw Dumbledore appear, he also saw Hermione disappear. Surely he wasn’t so optimistic as to assume that disappearance (alone) was something other than death.
Also, what plausible excuse could he present for having the Map while the Twins are Obliviated? Dumbledore is the one main character who definitely knows of the Map, so Quirrel would want to hide it from him.
Then, against, how did he know when “The crisis is over” and he could stop hurrying towards Harry?
With future intel, why hadn’t he prevented the disaster entirely? Why hadn’t he warned anyone? Why had he still gone out to search for the troll, in such a hurry that he burned through walls to get to it, if he knew he wouldn’t make it in time? Why didn’t he share the future intel with the other professors hunting the troll? That doesn’t sound like a time-loop.
Possible (although can paintings or ghosts move quickly enough to deliver the message in time?) but again, why did he stop?
Most of those can be explained away with reference to the others and the poor information available to Dumbledore. What stops Quirrel from saying he blasted off when he detected Hermione had been trapped on the terrace and the troll was immune to sunlight? There are no atomic clocks here. Similarly, if he had some surveillance system, he can say he stopped when Hermione died and there was no more need to hurry (alas); between the wards and the soulsplosion, there’s plenty of ways for someone like Quirrel to plausibly get the info without positing bizarre unique psychic bonds.
There are multiple levels to the wards, and we don’t know what Dumbledore or McGonagal do or do not know—I’ve pointed out that Dumbledore wasn’t even in the castle, it seems, and McGonagal has no access to phoenixes and is not a battle mage who can burn through ancient magical walls at the speed of flight.
Perhaps he was bored, or piqued at the distrust.
We know he admires and imitates Muggle technology—recall the very first class. A spy network is perfectly reasonable. Of course Dumbledore would disapprove and would check for its existence, but sacrificing a spy network seems like a small price to not be the culprit for murdering a little girl. He can always replace it or put in a different system.
I’m afraid out-of-universe reasoning is not really available to the characters. :)
He can claim she was nowhere near and it was not an emergency until she was trapped on the terrace and it became clear that something had gone terribly wrong.
For all we know, Dumbledore might have a hand in the Obliviation. And did Quirrel expect the Obliviation to be detected? One suspects not: he wasn’t expecting Harry to be there either.
Already explained.
“I could explain, but I fear the necessary graphs would make your head explode and neither Snape nor Dumbledore could follow my exact reasoning. As Mr Potter might say, ‘do not mess with time’.”
Him stopping is really not as hard as you think it is.
Again, consider the alternatives here. That he has a unique, unprecedented, unnamed, inexplicable, unknown-to-all-but-him-and-Potter (AFAIK) telepathic bond and also in conjunction with an elaborate theory about him trying to kill Hermione (why?) this explains some movements during a chaotic 2 minutes or less of troll-hunting based on finely-parsed counterfactuals of what he would and would not know where you suppose that characters would place high confidence in their deductions about an infamously devious, whimsical, highly-knowledgeable intelligent weirdo.
For what it’s worth, Dumbledore reasons with storybook logic.
The triggers you propose wouldn’t work, assuming that Dumbledore should be able to make a good estimate of Quirrell’s speed and the time he spent traveling. I also think that Dumbledore should have noticed when Quirrell stopped, since by then he had already returned to Hogwarts.
Fred and George spent quite a long time fighting the troll; if Quirrell had started his mad dash when the troll reached the terrace, when Hermione had her legs bitten off, or when Harry, Fred, and George reached the scene, he would have arrived before the end of the fight. I guess, theoretically, his vast, previously-undetected spy network could have noticed the battle at exactly the right time, but that seems implausible to me, and it would seem similarly implausible to Dumbledore. Quirrell could also have been triggered by Hermione’s death, but I suspect Dumbledore could falsify that one; if he had started when Hermione died, he wouldn’t have been able to cut such a huge swath of destruction through Hogwarts in the time between Hermione’s death and his stopping.
It’s possible he was triggered by the troll’s death, but that would make no sense; as far as he should know, the end of the troll means the end of the catastrophe. I suspect Dumbledore’s first guess should be that Quirrell had put a ward on Harry (despite Dumbledore’s orders otherwise) and he was therefore able to detect when Harry started to fight… however, if Dumbledore were to actually ask Harry about this, Harry would of course tell him that, no, Quirrell isn’t able to cast any magic on him, which would probably be enough of a hint to lead Dumbledore to the correct answer.
It’s hypothesized both in canon and in Methods that Harry and Voldemort might have a connection of some sort. So, it wouldn’t exactly be unexpected and inexplicable; indeed, it seems like it’s something that Dumbledore and McGonagall might rate as high-probability conditional on Quirrelmort theory. (And I can’t imagine that psychic bonds are unheard of in Methods-world.)
How would he? He was not with Quirrel nor was he presumably examining the Map (if he had it).
Not really? They spent maybe 30 seconds at the outside—it doesn’t take long to cast a bunch of spells and swing a sword once. In the real world, fights do not last very long. Only in movies do fights go on for entire minutes.
Dumbledore would have to ask, though, and why would he when he would expect Harry to be ignorant? I would also note Quirrel’s own explanation to Harry about a ‘cursed artifact’, which is a likely and also fully general explanation which Dumbledore could not compel a peer of his to explain his secrets, not in a culture like Magical Britain.
Based largely on the events at the end of Stone, which never happened in MoR; in MoR, the only basis for this speculation is Harry being a Parseltongue. A passed on ability doesn’t suggest a live physic link.
Do they? Everyone seems quite satisfied with the David Monroe theory.
We have no idea.
Ok, you’re right, there isn’t enough information to get past the prior implausibility of the hypothesis. I think the other characters should assume he placed tracking charms on Harry. Any explanation about tracking the troll or Hermione would result in him arriving earlier, and when questioned, the divination professor can say approximately when Quirrell started to move, which cross-referenced with Harry’s recollections shows that Quirrell’s actions correlate with Harry being in danger, not Hermione. However, I assume that these tracking spells can be detected, in which case, if another character attempts to detect these spells and finds none on either Harry or Hermione, the Quirrell has done something seemingly impossible. Given this, Quirrell should probably cast such a spell on Harry before this occurs to anyone.
The problem is that Quirrell can’t cast any spells on Harry. And, furthermore, Quirrell really doesn’t want Dumbledore to find this out—Dumbledore already knows of a certain other person with an unexpected inability to cast spells on Harry Potter, and I think the hint would probably be enough for him to put the two together.
Oh, good point, I had forgot about that. In which case… Dumbledore may not be able to guess the telepathic link due to prior implausibility, but he should realize that there is something odd going on, if it crosses his mind to investigate how Quirrell knew where to go.
Of course, this may not occur for a while if at all, as Dumbledore has plenty of other things to worry about, and the obvious suspect from his POV is Lord Malfoy.
I’ve tried to make it work as a Lord Malfoy assassination, but I can’t seem to make the pieces fit together, and I don’t think Dumbledore would be able to either… Of course, it would be an easy frame-job, should Dumbledore or anyone else be interested in that. I’m going to explain why, not to convince you, but to establish why Dumbledore probably won’t accept that so readily.
First, if it were Lord Malfoy, the assassination would doubtless be for honor, which means that it should be recognizably the work of the Malfoy family. That means death via snakebite. Such an obvious killing may affect Harry’s debt, or create a new blood debt in Harry’s favor, but as has already been demonstrated Lucius doesn’t care about that very much. A mountain troll… doesn’t really have very much to do with Lucius Malfoy. It doesn’t fit the pattern.
Second, the Marauder’s Map Confunding doesn’t make very much sense. Lucius could do a lot with an Imperiused professor, but indiscriminate Legilimency doesn’t seem like one of those things. So, he shouldn’t know about the Map, and definitely shouldn’t have erased it from Fred and George’s minds. That’s not necessarily a disqualifier, but it does mean that Lucius would have to be working with either Snape or Quirrell; I’ll talk about Snape later, but if Quirrell was involved we may as well consider it a Quirrell plot, even if he collected payment from Lucius on the side.
Third, it seems unlikely that Snape is involved. Dumbledore is not opposed to him pretending to be on Lucius’s side. Indeed, Lucius Malfoy trying to pull an assassination from under Dumbledore’s nose would act sufficiently in Dumbledore’s political favor that he might be inclined to let it play out, so long as he would be able to save Hermione at the last minute. This probably wouldn’t even cost Snape much—of course an assassination in Dumbledore’s own castle would be a long shot for Lucius. However, Snape didn’t tip Dumbledore off at all. Even if he suddenly hates Dumbledore, this wouldn’t make any sense for him.
Fourth, and finally, Lucius would have to somehow find a way to circumvent the Hogwarts wards. The dementor in the Humanism arc needed a special pass from Dumbledore in order to get through the wards. Since the mountain troll is the third most perfect killing machine, after the dementor, it’s not unreasonable to suspect that it would also require a special pass from the wards. This would be a problem for Lucius Malfoy and his cronies, even with the aid of Severus Snape or another Imperiused professor. For our benefit, this points the finger squarely at Quirrell, and his secret knowledge inherited from Salazar Slytherin who made those wards; it should merely baffle poor Albus, however.
Firstly, I’m pretty sure Quirrell did it, because (a) he did it in canon and (b) we know he’s voldemort and he’s trying to turn Harry dark (c) he tried to persuade Hermione to leave. But Dumbledore knows none of this, with the possible exception of (c).
Lord Malfoy does not hold absolute power, and even if he could avoid punishment for murder, it would cost him political capital, he would lose swing votes and so forth. But he is not stupid, and so might kill in an uncharacteristic way because it is uncharacteristic. Yes he would want some people to recognize his revenge, but some of the wiser wizards would realize it was him anyway, and he could privately confess it to intimidate his enemies while publicly denying it to minimize the fallout.
I think Fred and George are old enough to leave hogwarts and visit the nearby village, in which case they could have been ambushed there. Do we actually know whether Imperitused people can perform memory charms? He could also have got one of his allies to do this, either a teacher or one of the older students, although this would be more risky.
I’m not sure how the wards work, nor who has permission to alter them. There is at least one charm that affects only dementors, so its possible that the wards might be able to detect dementors but not trolls, but that’s just conjecture.
Finally, if there is no way this could have been organized by anyone but a Hogwarts professor, then the finger of blame points squarely at Quirrell, and I think Quirrell is smart enough to avoid that (e.g. if magical creatures cannot be sneaked past the wards, why not smuggle in a lion and cast spells on it to stop magic affecting it?).
Therefore, when Dumbledore looks at the evidence there is going to be sufficient doubt over who did it, and also the secrets of Salazar Slytherin will not be implicated. If Quirrell can devise a plan to break Belltrix out of prison, he can murder a girl without getting caught.
Not to say that Harry won’t realize it was him eventually, but only after more evidence, a lot of deduction and only a few chapters from the stories’ end :)