Federal officials who spoke with NBC News said it took agents a while to figure out the source. They did that by finding out where the messages were sent from — which cities, which wi-fi locations in hotels. That gave them names, which they then checked against guest list from other cities and hotels, looking for common names. That led them to Broadwell, they said, noting that the pattern coincided with her travel to promote her book.
FBI agents and federal prosecutors used the information as probable cause to seek a warrant to monitor Broadwell’s email accounts. They learned that Broadwell and Petraeus had set up private Gmail accounts to use for their communications, which included explicit details of a sexual nature. But because Mr. Petraeus used a pseudonym, agents doing the monitoring didn’t immediately uncover that he was the one communicating with Broadwell.
Rather than transmitting emails to the other’s inbox, Petraeus and Broadwell composed at least some messages and instead of transmitting them, left them in a draft folder or in an electronic “dropbox,” the official said. Then the other person could log onto the same account and read the draft emails there. This avoids creating an email trail that is easier to trace.