PROMTS: Avada Kedavra and past.
Severus entered the headmasters office in a desolate state. His expression, however remained neutral and did not portray his inner anxiety.
Wand in hand, he briskly strode past his fellow death eaters, towards the cowering Draco Malfoy. Pushing the teenage boy aside, he, himself stepped forward to complete what the young lad had been unable to do.
Memories of his own past filled himself as he stood in front of the wizard who had taught him so much and was even willing to sacrifice himself for the greater good. Remembering his instructions, he steadied his hand and slowly rose his wand to point it at the older wizards chest.
For a moment the world stood still and flash of uncertainness went through Severus's eyes.
"Severus, please," Dumbledore pleaded, urging him to do what he had to. The tone was unfamiliar to Severus and prompted him to look directly into the eyes of the wise sorcerer. He was truly desperate.
Severus took a deep breath. "Avada Kedavra," he muttered, knowing that he'd forever regret it.