I think nobody is credible, and certainly agree that Brennan and others are not. I'm not sure the truth will ever come out and I think an insider attack is just as likely or even more likely than an external hack. But an external hack is possible, not "impossible" at all. The same exact dumping of Exchange Server email into a file can be done locally or remotely. The file can be easily transferred in less than 87 seconds (and I have no idea where that number actually came from).
Totally agree.