The Avada Kedavra on the Astronomy Tower

[felicitys_mind]

[This post is an expansion of the first section of an essay arguing the Stoppered Death theory.  I needed more room over there to describe the background to that theory, so I moved the AK evidence here and vastly expanded it.  Read about the Stoppered Death theory here: http://felicitys-mind.livejournal.com/2616.html]

The Avada Kedavra Snape Cast at Dumbledore was Real and Instantly Ended Dumbledore's Time Amongst the Living

A challenge to the arguments that Snape did not cast a real AK at Dumbledore on the Tower or that he did yet Dumbledore did not die from the killing curse but rather from the fall to the ground.

The arguments:
 

• Snape didn’t hate Dumbledore, so his AK wouldn’t have been able to kill him
• The AK didn't blast Frank Bryce into the air, so it shouldn't have with Dumbledore
• Dumbledore’s eyes were closed, but the eyes of the other AK victims were open
• Dumbledore’s body was suspended mid-air for a split second, so it wasn’t an AK
• Harry wasn’t immediately released from the body-bind when the AK hit Dumbledore
• Dumbledore was holding a magical shield to his chest that blocked the AK
• Snape simultaneously cast a non-verbal spell, and the non-verbal trumped the AK
• There was a trickle of blood on Dumbledore’s dead face, and only living bodies bleed

How could Snape AK Dumbledore if he didn’t hate Dumbledore?

Two things are required to pull off an Unforgivable Curse: volition (the intent of the caster to cause the outcome-pain, control, or death) and sufficient magical power. Neither is dependent on the personal feelings of the curse-caster toward the target of the curse.

Fake Moody said an AK needed a "powerful bit of magic behind it," but he didn’t say the caster needed to hate the victim, and indeed it’s not likely that Death Eaters who cast Unforgivable Curses know most of their victims well enough to have developed personal feelings toward them. Certainly Fake Moody didn’t hate the spider he AK’d in class, and Bellatrix didn’t even know what she was casting the AK at when she killed the fox in HBP2 (“Just a fox" . . .”I thought perhaps an Auror.”).

In OP, Bellatrix said Harry's Cruciatus Curse against her did not cause pain because Harry didn't have the intent to cause pain, but intent is not dependent on the curse-caster’s personal feelings toward the victim. When Harry tried to Crucio Bellatrix, we read,

"Hatred rose in Harry such as he had never known before. He flung himself out from behind the fountain and bellowed, "Crucio!"

If hatred were the key to casting the Cruciatus Curse, then Harry should have caused unbearable pain to Bellatrix since he hated her and expected the spell to cause pain to her. But he didn’t cause pain because his hatred of Bellatrix was not “powering” the Unforgivable Curse.

In HBP1, we learned that Herbert Chorley, the Muggle Junior Minister, was impersonating a duck and had attempted to strangle three Healers at St. Mungo’s because of a “poorly performed Imperius Curse,” which means the person who attempted to Imperius Chorley either didn’t have the proper volition or sufficient magical power to it off. All through HBP, Draco was shown in a weakened state: his health was suffering, he wasn't keeping up with his homework, and he was confiding in and crying to Moaning Myrtle about a job he couldn’t do. Draco may possess the magical power needed to pull off an Unforgivable Curse, and given the pressure he was under from Voldemort, he certainly would have wanted to Imperius Rosmerta to help him, but during HBP, he didn't have the strength of mind to hold Rosmerta under the Imperius Curse (so Bellatrix was doing it, I think).

Moments after casting the AK at Dumbledore, Snape was confronted by Harry on the castle grounds; Harry attempted to cast the Cruciatus Curse on Snape, who repeatedly blocked Harry’s attempts and then restated the requirements to cast an Unforgivable Curse:

"No Unforgivable Curses from you, Potter!” he shouted over the rushing of the flames, Hagrid’s yells, and the wild yelping of the trapped Fang. “You haven’t got the nerve or the ability-"

Snape knew Harry hated him at that moment, but it wasn’t emotion Snape referred to as a requirement of casting the curse; rather, he was talking about volition (nerve) and magical power (ability). Even if Snape didn’t want to end Dumbledore’s life, he still would have been able to surmount his personal feelings to cast the curse.

Dr. Ronald Glasser, a doctor stationed in Japan during the Viet Nam conflict, in 1971 wrote 365 Days, a series of documentary sketches about American soldiers, medics, helicopter pilots, Vietnamese civilians, etc. It’s a wrenching book (still in print), and one of the most difficult chapters describes the suffering endured by the soldiers in the Army hospital burn ward where the worse cases were treated. I read the book years ago, but I haven’t forgotten the stories of severely burned soldiers who had to endure frequent treatments of hydrotherapy and mechanical debridement (scraping away of burned and necrotic tissue to reveal raw wounds and open nerves). The soldiers couldn’t be given high enough doses of narcotics to dull the pain for fear of addiction over the months of debriding treatments, and Dr. Glasser recorded the horror of the sessions as the soldiers screamed and sobbed and begged the medical personnel to stop. The doctors, nurses, and technicians had to steel themselves as much as the patients did for these treatments, knowing it was the only option that offered hope.

Severus Snape, able to both wound and heal, is a man who would have been able to perform the AK against his friend and mentor Albus Dumbledore in that situation. Neither wanted circumstances to fall out the way they did, but both knew Snape had to cast the AK because it was the only option that offered hope given Dumbledore’s condition and the need to preserve Snape to help Harry vanquish Voldemort.

When does the AK blast a human body into the air? Usually, it seems.

One of the persistent arguments against the idea that Snape's Avada Kedavra on the Tower wasn't "real" is that Dumbledore’s body trajectory was inconsistent with what we saw in Frank Bryce’s death. However, a review of passages in which the Impediment, Expelliarmus, and Avada Kedavra spells are used demonstrates that these spells do not produce consistent secondary effects, even when the same person is casting the spell. While this won’t convince anyone that Snape did cast the Avada Kedavra curse on Dumbledore on the AstronomyTower, it should certainly disprove the argument that Snape couldn’t have cast the Avada Kedavra because Dumbledore’s body was blasted into the air.

Impedimenta

The Impediment jinx impedes or stops an object from moving by temporarily freezing it. The spell sometimes lifts the target off his or her feet and sometimes does not.
 

• Madame Hooch used it against Harry after he hit Draco at a Quidditch match; Harry was “knocked over backward by the force.” (OP19) 

• Harry taught it to the DA, but they didn’t need to use cushions because they were only being frozen for a minute or two without falling over; after practicing the Impediment jinx, they pulled out the floor cushions to practice stunning (OP21)

 

• In Snape’s Worst Memory, James used it against Snape “who was knocked off his feet, halfway through a dive toward his own fallen wand.” (OP28)

 

• Two DE’s used it in the DoM, casting the jinx in unison against a group of three students: “Harry, Hermione, and Neville were all knocked backward off their feet. Neville was thrown over the desk and disappeared from view, Hermione was smashed into a bookcase and was promptly deluged in a cascade of heavy books; the back of Harry’s head slammed into a stone wall behind him . . .”(OP35)

 

• Harry used it against Lucius Malfoy who was “blasted off his back” (from his position on the floor) and sent crashing into a dais (OP35)

 

• Harry used it against Amycus and caused him to be lifted off his feet and slam into a wall and then over the wall (HBP28)

 

• Harry fired one over his shoulder against Amycus and Alecto who were running toward him on the Hogwarts grounds, “ . . . and miraculously his jinx hit one of them, who stumbled and fell, tripping up the other . . . .(HBP28)

Expelliarmus

A disarming spell that sometimes lifts the target off his or her feet and sometimes does not.
 

• “Snape cried: ‘Expelliarmus!’ There was a dazzling flash of scarlet light and Lockhart was blasted off his feet: He flew backward off the stage, smashed into the wall, and slid down it to sprawl on the floor.” (CS11)

 

• “[Harry] pulled out his wand and shouted, “Expelliarmus!” and just as Snape had disarmed Lockhart, so Malfoy found the diary shooting out of his hand into the air.” (CS13)

 

• “Harry reached his wand just in time. Lockhart had barely raised his, when Harry bellowed, ‘Expelliarmus!’ Lockhart was blasted backward, falling over his trunk; his wand flew high into the air; Ron caught it . . . : (CS16)

 

• “’Expelliarmus!’ he croaked, pointing Ron’s wand at them. Harry’s and Hermione’s wands shot out of their hands, high in the air, and Black caught them. (PA17)

 

• “’Expelliarmus!’ Lupin shouted. Harry’s wand flew once more out of his hand; so did the two Hermione was holding. Lupin caught them all deftly . . . (PA17)

 

• “’Expelliarmus [Harry] yelled-except that his wasn’t the only voice that shouted. There was a blast that made the door rattle on its hinges; Snape was lifted off his feet and slammed into the wall, then slid down it to the floor, a trickle of blood oozing from under his hair. He had been knocked out. Harry looked around. Ron and Hermione had tried to disarm Snape at exactly the same moment. Snape’s wand soared in a high arc and landed on the bed next to Crookshanks” (PA19)

 

• [During the first DA meeting] ”The room was suddenly full of shouts of ‘Expelliarmus!’: Wands flew in all directions, missed spells hit books on shelves and sent them flying into the air . . . Glancing around, he thought he had been right to suggest that they practice the basics first; there was a lot of shoddy spellwork going on; many people were not succeeding in disarming their opponents at all, but merely causing them to jump backward a few paces or wince as the feeble spell whooshed over them.  (OP 18)

 

• “Snape reacted so fast it was as though he had been expecting an attack: Dropping his bag, he plunged his hand inside his robes, and his wand was halfway into the air when James shouted, ‘Expelliarmus!’ Snape’s wand flew twelve feet into the air and fell with a little thud in the grass behind him. (OP28)

 

• “[Neville] pointed his wand wildly at the struggling pair [who were on the floor] and cried, ‘Expelliarmus!’ Both Harry’s and the Death Eater’s wands flew out of their hands and soared back toward the entrance to the Hall of Prophesy; both scrambled to their feet and charged after them . . . . “ (OP35)

 

• “The door burst open and somebody erupted through it and shouted, ‘Expelliarmus!’ . . . Then by the light of the Mark, he saw Dumbledore’s wand flying in an arc over the edge of the ramparts . . . Standing against the ramparts, very white in the face, Dumbledore still showed no sign of panic or distress . . . : (HBP27)

Avada Kedavra Curse

Also known as “the killing curse,” the Avada Kedavra is an Unforgivable Curse that instantly kills the person or animal it makes contact with; when it hits a non-animate object, it has variable effects. An AK Voldemort cast in Godric’s Hollow is recalled as a green light in Harry’s sketchy flashback memories. Readers have seen the Avada Kedavra Curse cast numerous times in the HP series, both verbally and non-verbally (w assume it’s an AK when the light is green and the caster's intent to commit murder):
 

• Babymort cast the curse on Frank Bryce in GF (verbal)
• Fake Moody cast the curse on a spider in GF (verbal)
• Wormtail cast the curse on Cedric Diggory in GF (verbal)
• Voldemort cast the curse five times in the MoM battle (once verbally at Harry and four times nonverbally at Dumbledore)
• Bellatrix cast the curse on a fox in HBP (nonverbal)
• Snape cast the curse on Dumbledore in HBP (verbal)

The Avada Kedavra always produces a flash or jet of intense green light out of the wand and is sometimes described as accompanied by a roaring, rushing noise (Frank Bryce in GF, spider in GF) but mostly not (Cedric in GF, all Voldemort’s AK’s in the DoM in OP, fox in HBP, and Dumbledore in HBP). Also, in the battle in Hogwarts at the end of HBP, a few jets of green light are mentioned, but no sound is described.

The secondary effects of the Avada Kedavra are hotly debated since readers who argued that Dumbledore was alive frequently pointed to the description of Dumbledore’s body being blasted into the air as proof that Snape must have uttered a different non-verbal spell that superseded the spoken AK. But a closer look at the descriptions of AK usage in the series actually gives support to secondary effects of the AK that are consistent with what happened to Dumbledore on the Astronomy Tower.  In other words, Frank Bryce is the exception to what an AK will do to a human, not the rule.

Frank Bryce (AK cast by Babymort):

“And then the chair was facing Frank, and he saw what was sitting in it. His walking stick fell to the floor with a clatter. He opened his mouth and let out a scream. He was screaming so loudly that he never heard the words the thing in the chair spoke as it raised a wand. There was a flash of green light, a rushing sound, and Frank Bryce crumpled. He was dead before he hit the floor.“ (GF1)

The AK makes contact as a jet of green light and kills instantly. In GF1, we saw Frank Bryce get hit with an AK. He had been standing up, and when the curse reached him, he was killed instantly and crumpled to the floor. His body wasn’t blasted into the air, but Babymort did not have his full strength as he told Wormtail, and he had been further weakened by the journey to Little Hangleton that day. Voldemort told his Death Eaters in the graveyard after his rebirthing that after failing to retrieve the Philosopher’s Stone, he decided to put immortality aside temporarily and settle for his old body and old strength. And we know he was weaker in his rudimentary Babymort body than in his full body because the magical, psychic connection between Harry and Voldemort strengthened considerably after Voldemort’s rebirthing.  Ergo, we have to take Babymort’s weakness into account to understand why Bryce's body wasn't blasted into the air.

The spider (AK cast by Fake Moody):

“ . . . [The spider] started to scuttle frantically across the wooden surface.

Moody raised his wand, and Harry felt a sudden thrill of foreboding.

‘Avada Kedavra!’ Moody roared.

There was a flash of blinding green light and a rushing sound, as though a vast, invisible something was soaring through the air-instantaneously the spider rolled over onto its back, unmarked, but unmistakably dead. Several of the students stifled cries; Ron had thrown himself backward and almost toppled off his seat as the spider skidded toward him.” GF14

What is interesting about the spider is that it was still moving after the AK killed it. The spider died instantly, but its corpse didn’t stop moving. The verb "scuttle" indicates the spider was moving on its own initiative across the desk before being hit with the AK, but the verb "skid" clearly implies the spider was not moving on its own initiative after being hit with the AK; rather, it was moving because of the secondary effect of the killing curse.  (Note: it was pointed out in the comments that the spider could have been skidding merely because it was already moving; however, the spider flipped over first, which seems to be a secondary effect of the curse.)

Cedric Diggory (AK cast by Wormtail):

“Harry lowered his wand slightly and glanced sideways at Cedric. Cedric shot him a quizzical look. They both turned back to watch the approaching figure.

It stopped beside a towering marble headstone, only six feet from them. For a second, Harry and Cedric and short figure simply looked at each other.

And then, without warning, Harry’s scar exploded with pain. It was agony such as he had never felt in all his life: his wand slipped from his fingers as he put his hands over his face; his knees buckled; he was on the ground and he could see nothing at all; his head was about to split open.

From far away, above his head, he heard a high, cold voice say, ‘Kill the spare.’

A swishing noise and a second voice, which screeched the words into the night: ‘Avada Kevadra!”

A blast of green light blazed through Harry’s eyelids, and he heard something heavy fall to the ground beside him; the pain in his scar reached such a pitch that he retched, and then it diminished; terrified of what he was about to see, he opened his stinging eyes.

Cedric was lying spread-eagled on the ground beside him. He was dead.

For a second that contained an eternity, Harry stared into Cedric’s face, and his open gray eyes, blank and expressionless as the windows of a deserted house, and his half-open mouth, which looked slightly surprised.” (GF32)

Harry’s hands were over his face when Cedric was AK’d in GF32, but Cedric had been standing next to Harry when he got hit. Harry heard "Avada Kedavra!" and then “heard something heavy fall to the ground beside him”; when Harry opened his eyes to look, he saw Cedric’s corpse, supine in a spread-eagled position. To be spread-eagled is to be in a position in which the arms and legs are fully extended away from the body. In other words, Cedric hadn’t crumpled like Frank Bryce. If a standing man dies instantly, causing his body to crumple, his legs will buckle (as Harry’s did a moment before Cedric was killed), and he’ll end up in a semi-sprawl, but he won’t end up flat on his back with his arms and legs fully extended. Considering the position of Cedric’s body and the fact that Harry heard something heavy fall to the ground beside him after the AK was cast, it's likely that Cedric had been thrown into the air with his limbs flailing (like a rag doll, as Dumbledore had been described). Unlike Babymort, Wormtail had his full powers when casting the AK, so Cedric's body was blasted into the air.

Voldemort cast five AK’s between pages 813-815 of OP36:
 

• #1 was a verbal AK cast at Harry:

 “’I have nothing more to say to you, Potter,” he said quietly. “You have irked me too often, for too long. AVADA KEDAVRA!’

Harry had not even opened his mouth to resist. His mind was blank, his wand pointing uselessly at the floor.

But the headless golden statue of the wizard in the fountain had sprung alive, leaping from it’s plinth, and landed on the floor with a crash between Harry and Voldemort. The spell merely glanced off its chest as the statue flung out its arms, protecting Harry.

‘What-?’ said Voldemort, staring around. And then he breathed, ‘Dumbledore!’” OP36
 

• #2 was a nonverbal AK cast at Dumbledore

 “Voldemort raised his wand and sent another jet of green light at Dumbledore, who turned and was gone in a whirling of his cloak.” (OP36)
 

• #3 was a nonverbal AK cast at Dumbledore

 “He sent another killing curse at Dumbledore but missed, instead hitting the security desk, which burst into flame.” (OP36)
 

• #4 was a nonverbal AK cast at Dumbledore

 “Another jet of green light flew from behind the silver shield. This time it was the one-armed centaur, galloping in front of Dumbledore, that took the blast and shattered into a hundred pieces . . . .” (OP36)
 

• #5 was a nonverbal AK cast at Dumbledore

 “ . . . one more jet of green light had flown at Dumbledore from Voldemort’s wand and the snake had struck.

Fawkes swooped down in front of Dumbledore, opened its beak wide, and swallowed the jet of green light whole. He burst into flame and fell to the floor, small, wrinkled, and flightless” (OP36)

When an AK hits an inanimate object, the object suffers physical damage, apparently depending on the type of material it's made of.  When Voldemort cast an AK at Harry in the graveyard at the end of GF, Harry ran behind a tombstone, which cracked when the AK hit it.

The fox (AK cast by Bellatrix):

“The harsh cry startled the fox, now crouching almost flat in the undergrowth. It leapt from its hiding place and up the bank. There was a flash of green light, a yelp, and the fox fell back to the ground, dead." (HBP2)

The fox is interesting because the passage is vague.  The fox "fell back to the ground, dead," yet it isn't clear if the fox was in the air when the AK made contact (since the fox was described as leaping up the bank) or if the AK blasted the fox into the air, and its dead body fell back to the ground.  There's no way to resolve this from the passage, but suffice to say, it doesn't contradict the idea that the AK blasted the fox into the air.

Dumbledore (AK cast by Snape):

“Snape gazed for a moment at Dumbledore, and there was revulsion and hatred etched in the harsh lines of his face.

‘Severus . . . please . . .”

Snape raised his wand and pointed it directly at Dumbledore.

‘Avada Kedavra!’

A jet of green light shot from the end of Snape’s wand and hit Dumbledore squarely in the chest. Harry’s scream of horror never left him; silent and unmoving, he was forced to watch as Dumbledore was blasted into the air. For a split second, he seemed to hang suspended beneath the shining skull, and then he fell slowly backward, like a great rag doll, over the battlements and out of sight.” (HBP27)

[Thirty minutes passed by Harry’s estimate.]

“He and Hagrid moved, dreamlike, through the murmuring crowd to the very front, where the dumbstruck students and teachers had left a gap.

Harry heard Hagrid’s moan of pain and shock, but he did not stop; he walked slowly forward until he reached the place where Dumbledore lay and crouched down beside him. He had known there was no hope from the moment that the full Body-Bind Curse Dumbledore had placed on him lifted, known that it could have happened only because its caster was dead, but there was still no preparation for seeing him here, spread-eagled, broken: the greatest wizard Harry had ever, or would ever, meet.

Dumbledore’s eye were closed; but for the strange angle of his arms and legs, he might have been sleeping. Harry reached out, straightened the half-moon spectacles upon the crooked nose, and wiped a trickle of blood from the mouth with his own sleeve.” (HBP28)

Dumbledore’s body was thrown into the air and over the ramparts at the top of the Astronomy Tower. Dumbledore’s AK’d body at the bottom of the tower was described as being supine in a spread-eagled position, just as Cedric’s had been. Since both Dumbledore and Cedric had been hit with AK’s and both ended up on their backs in a spread-eagled position, this is confirmation from Rowling that what we saw happen on the tower is a bona fide reaction to the Avada Kedavra curse and that Cedric's body was thrown into the air.  Snape had his full powers when casting the AK, so Dumbledore's body was blasted into the air.

What about Dumbledore’s closed eyes?

Dumbledore’s eyes were closed when Harry viewed his body at the bottom of the Tower whereas the eyes on the corpses of Cedric and the Riddles were open. But this has nothing to do with the AK itself, but rather indicates whether the victim’s eyes were open or shut when the curse made contact.

The Riddles looked as if they had been frightened to death. Frank Bryce was looking at Voldemort and screaming when he died, so it’s a good bet his face looked the same as the Riddles. Cedric and Harry were puzzled that the TriWizard Cup had turned out to be a portkey that took them to a graveyard; they were both watching Wormtail and his bundle walk toward them when Harry was overcome with pain from Voldemort. Cedric would likely have glanced at the stricken Harry before returning his gaze to the approaching Wormtail, which is consistent with Harry’s description of Cedric’s dead face as appearing slightly surprised.

In contrast, Dumbledore was not caught off guard, nor was he afraid, nor was he unsure of what was happening because he wanted Snape to cast the curse and, in fact, was pleading with Snape to cast it. I firmly believe Dumbledore closed his eyes before Snape cast the curse because he knew it would be harder for Snape to do it if Dumbledore was looking at him. That’s why Dumbledore’s eyes were closed when Harry saw his body.  Also, the fact that Harry described Dumbledore as appearing to be sleeping is Rowling's way of assuring the reader that Dumbledore was at peace when he died.

What about the split second Dumbledore was hanging in the air before falling?

Why did Dumbledore seem to hang in the air for a split second before slowly falling backwards out of Harry’s sight?  We learned about non-verbal spells in HBP, so I wouldn’t discount this explanation: after marshaling the volition to cast the AK that ended Dumbledore’s life instantly, Snape non-verbally held his body up briefly. This could even have been done subconsciously, harking back to PS/SS when Hagrid asked Harry if he’d ever “made things happen” when he was angry or upset. Snape was both at that moment: angry at Draco for bringing them all to that point, and upset by the passing of his friend and mentor.

I highly recommend the following insightful essay by Helen Ketcham, who argues:

“ . . .[if] Snape’s conduct can be shown to be consistently congruent with Dumbledore’s values, principles and goals, perhaps we may infer that even such a shocking death, though a tragedy, may still not be a betrayal. My hope is to add just enough conjecture, not too wildly unsupported by the text, to the scraps and glimpses we have of Snape’s life to suggest some reasons why Professor Dumbledore persisted, and rightly so, in valuing and trusting him.”

'Good Snape' is not a 'Square Circle' By H.M. Ketcham
http://www.hogwartsprofessor.com/home.php?page=docs/GoodSnape2

Was Harry released from the body-bind jinx when the AK hit Dumbledore?

Yes.  The passage was narrated from Harry's point of view, and Dumbledore’s death was surreal for Harry. It could be that Snape held up the body for a split second (I will even say it’s likely he did), but the rest of the description of Dumbledore’s fall is not related to spells cast or not cast since the descriptions of Dumbledore’s and Sirius’s “death falls” are so similar:

In OP35: “Harry released Neville, though he was unaware of doing so." . . . “It seemed to take Sirius an age to fall. His body curved in a graceful arc as he sank backward through the ragged veil hanging from the arch.”

In HBP27: "For a split second, he seemed to hang suspended beneath the shining skull, and then he fell slowly backward, like a great rag doll, over the battlements and out of sight."

One argument is that Harry remained frozen for a few seconds after the AK hit Dumbledore and that Harry was only released from the Full Body-Bind when Dumbledore’s live body hit the ground and killed him. However, as Harry, who had been pinned to the wall by Dumbledore’s nonverbal spell, watched Dumbledore’s body fall over the ramparts, he “felt as though he too were hurtling through space,” so Harry experienced a sense of movement before Dumbledore’s body hit the ground.  Harry then realized what had been "holding him against the wall was not magic, but horror and shock."

A short time later, Harry and Hagrid were described as moving “dreamlike” toward Dumbledore’s body:

“He and Hagrid moved, dreamlike, through the murmuring crowd to the very front, where the dumbstruck students and teachers had left a gap.

So the slow-motion description of Dumbledore’s falling body, Harry’s sympathetic falling sensation, followed by his realization that shock and horror (not the spell) were holding him against the wall, and the “dreamlike” description of Harry as he walked toward the body are telling us about Harry’s state-of-mind, not that Dumbledore hadn't been killed by the AK.

Could Dumbledore have been holding up a shield so that the AK was blocked and he really died from the fall?

The trouble with this imaginative theory advanced by Red Hen is that Rowling wouldn’t cheat by using a device or spell we’d not properly been introduced to first. She’s playing by the rules, so she can’t fire a gun without showing us the gun in advance. That’s one big problem with the “magical shield that can block an AK” theory. Yes, we’ve seen an AK cast at Harry hit and crack a gravestone he ducked behind, but that’s not showing us a gun. That’s saying, well, no I didn’t show you a gun, and in fact, I’ve told you there is no such gun, but I showed you a thin metal tube, and my brilliant character made it into a gun without my telling you. That would be a cheat, and Rowling wouldn’t do it.

All the evidence suggests that the AK was real and Dumbledore took it directly; the shield theory proposes a highly problematic solution to what boils down to the curious split-second that Dumbledore appeared to be hanging in mid-air.  A troublesome consideration is that a solution to a Rowling plot mystery should answer the question “What happened?” without turning the solution itself into a mystery in its own right.  How would Dumbledore know about this fabulous protective device when no one else in the Potterverse knows about it?  Would Dumbledore not have at least shared it with his OotP colleagues and MoM Aurors, etc.?  Is it remotely likely that Death Eaters would not know about this amazing trick?  It just isn't credible that in the time the AK has existed and been observed to hit inanimate objects without passing through to living people behind those objects that Dumbledore is the only person to have thought to construct a wearable protective shield that blocks an AK.

Moreover, the argument that Dumbledore was holding his hand to his chest on the Tower to keep this device in place is very weak.  Why did he suddenly need to hold on to it when he hadn't in the previous three hours when he was Apparating, swimming, moving through the cave, etc.  After drinking the green potion, Dumbledore was so weakened Harry had to half-carry him, so wouldn't Harry have felt the shield?  ("And pulling Dumbledore’s uninjured arm around his shoulders, Harry guided his headmaster back around the lake, bearing most of his weight” . . . .“back under the starry sky, Harry heaved Dumbledore onto the top of the nearest boulder and then to his feet. Sodden and shivering, Dumbledore’s weight still upon him”  (HBP27))  And if Dumbledore wasn't wearing the shield in Hogsmeade but was wearing it on the Tower, when did he get it?

It's more plausible that Dumbledore had his hand on his chest because he was 150 years old, had just drunk 12 goblets of poison, and was dying.

For more background to this shield theory and a truly wonderful historical connection between Horace Slughorn and American magician Horace Goldin, please read Gumshoe's, "Dumbledore is not Dead" essay at TLC: http://www.the-leaky-cauldron.org/#scribbulus:essay:141

What about a non-verbal spell that trumped Snape's verbal AK?

Like the magical, invisible shield, that would be a cheat because there aren't any set-ups for it.  There is no evidence that it's possible to cast a non-verbal and a verbal spell at the same time, let alone cast them simultaneously and have the non-verbal trump the verbal (as Jeremy Able at Eating Words noted, that's asking a lot--even for the brain of Severus Snape). Try shouting "Avada Kedavra!" while thinking "Wingardium Leviosa!" at exactly the same moment.  Remember that your verbal killing curse has to produce all the visual effects associated with the AK (a green light or jet) and hit but not harm the target, while at the same time, your non-verbal levitation charm has to produce the desired magic by holding up Dumbledore's body, but only for a split-second.

Moreover, when a spell is supposed to produce a distinctive optical effect and it does, then the evidence is there that the spell was cast correctly and hence is efficacious. For instance, when Harry was trying to produce a patronus, his first few attempts were silvery, formless wisps that quickly dissolved. When he finally managed to produce one, it was a stag that cantered around the room. So Snape's AK on the Tower was effective since Snape's wand was pointed directly at Dumbledore and Snape produced a jet of green light that hit Dumbledore squarely in the chest.  It sure looked like a very powerful AK considering the reaction of Dumbledore’s body. We know of only one other spell that produces green light, and it made Ron Weasley burp slugs. The spell that hit Dumbledore blasted him into the air.

What about the trickle of blood that Harry wiped from Dumbledore’s mouth?

CSI fans like me know corpses don’t bleed because circulation has stopped, but the wife of a pathologist on a BNU HBP forum asked her husband if Dumbledore’s just-dead corpse could have bled if his teeth clamped down on his tongue or lip when his body hit the ground. The answer was yes.

Conclusion

Looking over the evidence, there’s only one conclusion possible IMO-Dumbledore died the instant Snape’s AK made contact.

For another demonstration of the realness of the AK with excellent arguments, please read "A Dozen Reasons Why Albus is Deader than a Dumbledorenail at TLC: http://www.the-leaky-cauldron.org/#scribbulus:essay:139.