"I was in Gringotts," he continued, "Voldemort," Snape hissed at his use of the name, "was in Gringotts. With Draco’s parents, and Bellatrix Lestrange. They were looking for something in the Lestrange vault - something they couldn’t find. And I was furiously...  he was furious," he clarified, "and he said... he said that he was going to kill Draco," Snape’s expression didn’t change.