Although Dumbledore was already going to die from wearing Marvalo Gaunt's ring, which is the second Horcrux, there is a much deeper reason why he had to die, especially in the hands of Snape, instead of dying from the curse or at the hands of the
Snape took the fall instead at Dumbledore's insistence. But, that's not all. Dumbledore was also aware that he wouldn't be alive for long because he had been cursed by the Horcrux ring. Instead of suffering a painful death, he urged Snape to end his misery.
But there were parts of the story Harry didn't know, including that Dumbledore was already dying and had asked Snape to kill him when the time was right.
Snape vowed to watch over Draco, Narcissa's young son, in his “attempts to fulfill The Dark Lord's wishes” as well as “carry out the deed The Dark Lord has ordered” should Draco be unsuccessful. The Dark Lord's wishes included Dumbledore's murder. More events occur from then on that culminate in Dumbledore's demise.
It's clear that Dumbledore did both ask and expect Snape to kill him, and this was always his plan.
Later in the year, McGonagall duelled with Death Eater Alecto Carrow during the Battle in the Astronomy Tower and later learned of Snape's murder of Dumbledore. McGonagall was initially appointed as Headmistress, but was demoted after Voldemort took control of the school and placed Snape as Headmaster.
Knowing that Snape has been on the Dumbledore's side for all seven of the Harry Potter books reveals him as an extremely brave man and a truly skilled spy. Snape has had to face and deceive the terrifying Lord Voldemort constantly.
12. Snape's Last Words. In the [Deathly Hallows] book, Snape's dying words to Harry were "Look at me". Right then we did not realize the significance of his words but in the very next chapter when Harry goes through Snape's memories in the Pensieve, he comes to know how much Snape loved Lily.
So, Voldemort had to kill Snape for the wand's allegiance to switch. Voldemort knew he couldn't cast Avada Kedavra with the Elder Wand to kill its master, so he ordered Nagini to be the one who killed Snape. In reality, the Elder Wand belonged to Draco, as he was the one to disarm Dumbledore in the Astronomy Tower.
In her estimation, in an attempt to protect the true Harry's identity, Snape sacrifices Hedwig, thus keeping the other Death Eaters off his scent albeit for only a short time.
All lessons at Hogwarts were suspended and all examinations were postponed, every student (with the exception of those taken from school early and Draco Malfoy) was present, as were all Professors, excluding Severus Snape. Dress robes were worn.
In order to conjure the avada kedavra curse, you have to want to kill your victim. We all know that Voldemort could easily kill a child without an ounce of remorse... but not Snape. Snape didn't want to kill Dumbledore, and this was why the spell was blue instead of the usual green.
Voldemort intentionally made six Horcruxes, but when he used Avada Kedavra on Harry, he unintentionally created a seventh Horcrux. Instead of dying, Lily's love for Harry created a counter 'curse' known as Sacrificial Protection and saved Harry.
Three reasons, really: firstly, as part of Harry's transition from boyhood to full blown adult wizardry, the death of Dumbledore represents the point at which Harry is fully exposed to the fight against Voldemort - his insistence on not briefing Prof McGonagall (as the new head of Hogwarts) on Dumbledore's final ...
Because Voldemort literally took over the Ministry of Magic. And immediately after Dumbledore's death, Snape disappeared with the rest of the Death Eaters from the Astronomy Tower. The Ministry had a hard time tracking any of the key players in Voldemort's ring.
Professor Snape is dead on Voldemort's orders, and Harry saw it all. In his dying moments, he told Harry to take his memories and look at him one last time. Voldemort's voice then sounded through the corridors, challenging Harry to meet him in the Forbidden Forest in an hour. This is the end.
During his final confrontation with Voldemort, Harry knew that he (Harry) was the Elder Wand's true master. He again cast Expelliarmus, ejecting the wand from Voldemort's hand into his own as the Killing Curse rebounded off his body, fatally striking Voldemort.
Defeating The Dark Lord with his signature spell
Disarming is about defence, not murder. Voldemort was a killer, Harry was not. It was an important distinction for Harry, who had learned so much about Voldemort and seen first-hand the ways in which they were similar.
It's a word that gained so much more clarity and tragedy after Harry Potter and the Deathly Hallows revealed that the nefarious Professor Severus Snape was actually serving a nobler cause: protecting Harry from Voldemort out of love for Snape's childhood friend Lily Evans.
He is also revealed to be a double agent for Albus Dumbledore and the Order of the Phoenix. But many people forget that he also invented a number of spells. In the Harry Potter movies, Snape came up with the Sectumsempra curse when he was a student at Hogwarts, and it's known to cause painful lacerations on the target.
Bellatrix Lestrange
"What will happen to your children when I've killed you?
Similarly to Harry, Snape's patronus represents a person. In the memories he gives Harry before his death, Snape shows Dumbledore his patronus, using the form to prove his love of Lily Potter, Harry's mother. This indicates that Lily also had a doe patronus.