"Charlie's in Romania studying dragons, and Bill's in Africa doing something for Gringotts [bank]," said Ron. "Did you hear about Gringotts? It's been all over the Daily Prophet, but I don't suppose you get that with the Muggles - someone tried to rob a high security vault."
"Really? What happened to them?"
"Nothing, that's why it's such big news. They haven't been caught. My dad says it must've been a powerful Dark wizard to get round Gringotts, but they don't think they took anything, that's what's odd. 'Course, everyone gets scared when something like this happens in case You-Know-Who's behind it."
(Harry Potter and the Sorcerer's Stone)
Does the highlighted 'it' indicate ‘someone’ whose sex is unknown, or is it an anticipatory "it" (dummy it) for ‘a powerful Dark wizard to get round Gringotts’?