Authenticity
I don't understand why CIA and the media put such emphasis on the question of authenticity when a new Osama or Zawahiri tape comes along. The question would make good sense for a tape that came into CIA anonymously, 'over the transom'. It's totally irrelevant for a tape broadcast by al-Jazeera. Their own sources believe it's authentic, and their audience will believe what it says. If it agrees with Osama, the effect will be identical regardless of who owns the larynx that produced the sound. If it disagrees with Osama in any meaningful way, we can be sure that Osama himself will counter it quickly. So we don't need to check its authenticity at all. For 100% of practical purposes, it's authentic.