Didn't the email say he learned this information when the guy came into his office and told him?
I could be wrong but I think that was the operating assumption. I guess it could have come from a case file or something, but from my reading, the guy told him.
Edit: He said that friends told him about the raid, but the client told him about the sales. So shouldn't the information about the sales be confidential (he claims it is in the email).