I don't know quite how to read this WaPo story about Paula Broadwell as a sort of femme fatale who sent threatening emails to a woman described as "close" to Petreaus.

In one way, it's self serving - an apparent effort by Petreaus partisans to salvage at least some of his reputation. But it also explains why the FBI got involved in the first place:

The collapse of the impressive career of CIA Director David H. Petraeus was triggered when a woman with whom he was having an affair sent threatening e-mails to another woman close to him, according to three senior law enforcement officials with know­ledge of the episode.

The recipient of the e-mails was so frightened that she went to the FBI for protection and help tracking down the sender, according to the officials. The FBI investigation traced the threats to Paula Broadwell, a former military officer and a Petraeus biographer, and uncovered explicit e-mails between Broadwell and Petraeus, the officials said.

When Petraeus's name surfaced, FBI investigators were concerned that the CIA director's personal e-mail account had been hacked and that national security had been threatened. The officials said further investigation, including FBI interviews with Broadwell and Petraeus, led to the discovery that the two were engaged in an affair.

The identity of the woman who received the e-mails was not disclosed, and the nature of her relationship with Petraeus is unknown. The officials said the woman did not work at the CIA and was not Petraeus's wife, Holly. The law enforcement officials said the e-mails indicated that Broadwell perceived the other woman as a threat to her relationship with Petraeus.

Attempts to reach Broadwell and her relatives have been unsuccessful, and she has not made a public statement since she was linked with Petraeus on Friday.

All three senior officials who described the impetus for the investigation spoke on the condition of anonymity because aspects of the inquiry are ongoing.

There has been speculation that the FBI was actually investiating Petreaus for something else -- something corrupt and/or illegal - and accidentally stumbled across the affair. That doesn't track with what we know of Petreaus but an older man in love will do a lot to hold on to a younger woman.