Before Severus Snape Kills Dumbledore, Dumbledore Paralyzes Harry And Throws The Invisibility Cloak On Him
Before Snape said the decisive words — Avada Kedavra, the killing curse — Dumbledore actually cast an immobilizing spell on Harry and threw the invisibility cloak on him so that he’d not intervene and not be seen by anyone in the Astronomy Tower. Unlike in the movie, where Harry just stood on the lower floor and stared.