Researchers traced the phishing link back to a bitly account that wasn't password protected. When they saw the other links in the account, they were able to decode the email address each link corresponded to. This unveiled that gaining access to Podesta's emails was part of a coordinated attack against the Clinton campaign. See http://motherboard.vice.com/read/how-hackers-broke-into-john...
The second question is one of attribution (i.e. "Who did it?"). That's harder. I believe it was the Russians, but that's based more on faith in the U.S. and British intelligence services getting this one right than a smoking gun linking back to the Kremlin.
The second question is one of attribution (i.e. "Who did it?"). That's harder. I believe it was the Russians, but that's based more on faith in the U.S. and British intelligence services getting this one right than a smoking gun linking back to the Kremlin.