I'm writing a story where one man says to another man in German, "I know who you are." They only just met, and they wouldn't use "du". Is this right: "Ich weiss wer Sie sind"?
And does it need a comma after "weiss"?
EDIT: They just met. They are spies, and both are undercover. The man speaking means he knows the other man is a spy, and he thinks he knows which side the other man is working for. He doesn't mean he knows his name, but he knows his role.