A normal vampire wouldn't be able to move under Derek's pressure.
It was an unspoken order that they all understood and never broke. Thanks to Derek's superiority, he had that superior aura that no vampire could defy but this one, he wasn't normal.
This psychotic vampire shouldn't have been able to move due to Derek's pressure. Not only that, Derek held him firmly so it was a given that he stayed still but he didn't.
His 'will' had been compromised by some sort of spell. Now, he was laughing like a maniac.
"Finally!" he laughed. "That delicious blood. It tastes so good! I want more!" He attempted to bite Susan for the second time but Derek didn't give him a chance and instantly snapped his neck.
Vampires couldn't be killed unless they were attacked by specific weapons. Derek snapped his neck, knowing that I'm a few minutes, he would wake up but this psychotic vampire had lost his chance.
