Voldemort killed Snape in Harry Potter And The Deathly Hallows Part 2 using his Horcrux snake
Speaking only of the films, the Sectumsempra spell was different when used by Voldemort and Harry. When Harry used it on Draco, it was more of a hit than a slash, and the cut was all over his torso. However when Voldemort used it, he slashed and caused only one cut on Snape's throat.
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.
Instead, Voldie threw Nagini at Snape. Nagini was a very large snake and she bit into the side of Snape's neck and tore his jugular, and he died of blood loss very rapidly. If he had not done he would probably have died of the venom anyway.
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.
He was also a descendant of Slytherin himself, and could speak parseltongue. These are, of course, obvious signs that he should be placed in Slytherin.
Although Voldemort is currently using the wand, he notes that it doesn't behave as it should for him. By killing Snape, he hopes that it will change its allegiance to him. However, he doesn't want this to backfire (as we see it does when he tries to kill Harry, the Wand's true owner, with it).
He was on the point of collapse when it happened,” Rowling said. “Dumbledore didn't want to lose his wand at that point and Draco disarmed him. So that meant that the wand gave Draco its allegiance, even though Draco never knew it, even though Draco never touched it.
He was the most accomplished at Legilimency. No one could prevent Voldemort from looking inside their mind. Expect Snape. This shows Severus' abilities against the Dark Lord, making it clear that Severus was the more superior of the two.
Why doesn t Harry use Avada Kedavra on Bellatrix? Harry didn't use that spell because he cannot bring himself to kill anyone. He is not a killer.
When Snape killed Dumbledore. In probably the most shocking twist of the series, Snape cast the unforgivable Avada Kedavra curse on Hogwarts' beloved headmaster.
For using Dark Magic, albeit unknowingly, to cause serious harm, Snape sentences Harry to detention every Saturday until school ends.
Although Snape may not have projected his memory of James onto Harry, he still would have been predisposed to dislike him by virtue of him being James Potter's son. Harry being in Slytherin would not have changed this fact.
But when they went to Hogwarts, everything changed. The pair were parted when the Sorting Hat placed Severus in Slytherin and Lily in Gryffindor, and while Lily thrived in her new, magical life, Snape was essentially placed in close quarters with the likes of Lucius Malfoy, Avery and Mulciber.
Harry Potter came very close to being sorted into Slytherin before he persuaded the Hat to sort him into Gryffindor. Yet the spectre of Slytherin haunted him for some time afterwards, becoming particularly potent in Harry Potter and the Chamber of Secrets, when he was rumoured to be the heir of Slytherin.
At one point, Snape is named as a Death Eater by Igor Karkaroff, but Dumbledore comes to Snape's defence, claiming that although Snape had indeed been a Death Eater, he changed sides before Voldemort's downfall and turned spy against him.
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.
We know, by way of The Prince's Tale chapter in Deathly Hallows, that Snape turned on Voldemort when he realized that his master meant to kill Lily Potter. He goes looking for Dumbledore, and they have this exchange: “Hide them all, then,” he croaked. “Keep her — them — safe.
The darkest of the Dark Arts, Harry Potter unforgivable curses are the Cruciatus Curse, the Imperius Curse, and the Killing Curse. Although the curses are highly illegal, Harry using Unforgivable Curses happened, but he uses them once he was thrust into the Second Wizarding War.
None of the good guys dare use the Killing Curse throughout the events of the movies and books, no matter how high the stakes and how difficult things are. But Ron Weasley is the exception, giving it a go in the Deathly Hallows: Part 2 movie when himself and Hermione look destined to die via Nagini.