Voldemort killed Snape in
Voldemort killed Snape just to cover all his bases. Murdering him was unnecessary, as the previous owner of the Wand needs to be merely defeated, but Voldemort didn't want to leave any loopholes.
Erroneously believing Snape is the master of the Elder Wand and that Snape's death will make him the master of the Wand, Voldemort kills Snape by having his pet snake Nagini bite him through the neck.
Since he believed Snape to be the master, he figured it was safer to use other means. And he had probably already just discarded every other wand he'd used by that point because he had the Elder wand. So Snape would be able to give the memory to Potter, and still die; the killing curse wouldn't allow the progression!
By the time Voldemort got to Snape, he was already using the Elder Wand, getting it from Dumbledore's grave. Voldemort wanted to kill Snape because he (wrongly) figured that Snape is the new owner.
Voldemort thought Snape was the owner of the Elder Wand. Using Avada Kedavra while the Elder Wand was resisting Voldemort was already a risky business, but using it against the true owner would be suicide (as Voldemort would find out when he used the Elder Wand against its true owner: Harry).
However, Draco was ordered by Voldemort to kill Dumbledore. Lestrange saw this as an opportunity to test Snape's loyalty and while making this vow to always watch over Draco, Lestrange forced Snape to agree to killing Dumbledore himself in case the youngster was unable to do so.
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.
Avada kadavra spell can be blocked by objects like statues, etc. (OoP). Now, Voldemort had already split his soul into different parts i.e. horcrux. So basically he had become immortal and therefore using the spell would not harm him.
Harry's scar had hurt during Arrival Feast because of Quirrell's connection to Voldemort; Snape was then talking to Quirrell, allowing Voldemort, from the back of Quirrell's head, to sense Harry's presence.
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.
At the end of Book 6, “Half-Blood Prince,” Draco disarmed Dumbledore before Snape killed Dumbledore. “And that meant he conquered him, even though Dumbledore was very weak at the time, he was very ill. He was on the point of collapse when it happened,” Rowling said.
No. Albus Dumbledore did not intend for Draco Malfoy to disarm him. 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 and understood. . . .
Quirrell didn't use the Killing Curse on Harry, because Voldemort said “use the boy” to get the Sorcerer's stone from the Mirror of Erised. If Quirrell had killed Harry right away, he would have lost the chance to get the stone.
Though Harry encountered many opportunities that deemed Avada Kedavra necessary, it remains as one of the Unforgivable Curses Harry Potter never cast. For one, he viewed the spell as an immoral practice commonly used by users of the Dark Arts.
Because the killing curse can be blocked. In the books, Dumbledore blocks it... with Fawkes. Because when you intentionally kill someone, you destroy your own soul, then again Dumbledore is in King's Cross station just like fetus Voldemort, so maybe he's there because he actually did kill his sister.
Other Favorite Spells
Plus, there were some votes for Obliviate (erases memory), Silencio (silences someone or something), Homonculus Charm (reveals someone's true identity and location), and Levioso (levitation, and some fans say that this is Ron Weasley's signature spell).
He would always resent Harry for being James' son instead of his. Snape even said that he didn't want anyone to find out that he was protecting Lily's child, “especially Potter's son” (pg. 679 of Harry Potter and the Deathly Hallows) because of his hatred for James.
Nonetheless, despite her initially benevolent nature, Nagini's blood curse eventually turned her into a snake permanently. Though it is unknown if she became evil as a result of that, or was turned evil as a result of Voldemort turning her into a Horcrux. As a snake, Nagini was completely loyal to Lord Voldemort.
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.
Gaunt's ring
After retrieving the ring Albus Dumbledore himself fell victim to a curse that, even when contained, would likely have killed him within the year. Once rendered defunct as a Horcrux, the stone was placed inside a Golden Snitch and left to Harry Potter in Dumbledore's will.
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.
Dumbledore asked Snape to kill him so that he'd be spared the indignity and pain that were sure to follow.