Disclaimer: I am not J.K. Rowling.
Severus Snape walked up to the Astonomy Tower in his Death Eater robes and mask. His hand grasped his wand, as he stared at his fool of a headmaster.
"We've got a problem, Snape," said the Carrow bastard, Amycus, "the boy doesn't seem capable-"
But then Albus Dumbledore spoke.
"Severus . . . "
He was pleading, and Severus knew what that was and hated him for it. It did not have to come to this. It didn't. It was the old fool's own damn fault.
" . . . please . . . " Albus added.
Severus was angry at that man, and did as was ordered by the man he served.
"Avada Kedavra!"
A jet of green light flew from his wand, and hit Albus. Severus turned away; he didn't want to see the old man fall to his death.
"It's over!" he yelled at the others. "Let's go!"
He seized Draco Malfoy, and left the tower.
But as he walked his mind wandered. He knew that killing Albus Dumbledore had many advantages for him. But he still couldn't believe he had done it.
All he thought now was that he swore that with every soul of his being that if he had to go through all this, his enemy would fall and never return. . . .