After Dumbledore was killed in the Astronomy Tower, Snape and the rest of the Death Eaters decided to flee the scene as their task was accomplished. However, as they tried to escape, the members of the Order of the Phoenix and Dumbledore's Army tried to stop them, and a fight ensued. Eventually, all the Death Eaters managed to escape the castle, and they lit fire to Hagrid's hut, Harry tried to attack Snape and found out that he was the Half-Blood Prince, but they all finally disapparated Hogwarts.