How does Harper discover that the killer has access to multiple accounts and passwords? How did the killer gain access to them?

Harper discovers the killer writing on the EROS system under the alias "Levon". This is not the account he was using previously, which gives Harper the impression that the killer has access to EROS account names and passwords. Harper assumes that this is why the killer thanked Turner in his note. Somehow, the killer was able to get a list of names and passwords from Miles Turner.