Why shouldn't it be the PR person? Someone at the level of Jay Carney is ostensibly more than just a mouthpiece, but someone who gathers the information and weighs in on what's useful and relevant to disseminate to the press. This isn't always a nefarious thing; sometimes employees have incomplete information but aren't in a position to confirm it with the executives.
At this phase, where the story has run and the damage has been done -- the response should be done by Carney. Take the rebuttal to Mr. Olson, for example. That revelation is absolutely not something that should be revealed by Mr. Olson's boss or a coworker. First of all, just because you're an engineer doesn't mean you have all of the facts. The PR person is in a position to collect the facts, including whether or not it's legal to reveal Mr. Olson's reason for termination, and confirming that reason for termination with HR. Even Mr. Olson's boss wouldn't have that same level of confirmation.
The other advantage of having Carney make this response is that you can be sure that this is, for better or worse, the official company response. If instead, this was a blog post by Mr. Olson's co-worker calling him out for being a fraud...and the reaction to it was negative...then Amazon could pedal back and say, "Oh well that co-worker blogged something he shouldn't have and now he is being punished".
But since the condemnation of Mr. Olson has come straight from Mr. Carney, any backlash will be rightly the reaping of what Bezos, Carney, and all their lawyers have sowed.
edit: FWIW, a non-anonymous redditor is saying that he knows Bo Olson, personally, and says "I can assure you that Bo was not the one defrauding vendors that was another employee in the same department"...it strikes me as improbable that Carney (again, not just Carney, but Amazon's lawyers and HR) would get this wrong. But if they did...it's going to be a great backlash, and a much more lasting one than had this allegation come from someone other than Carney or Bezos himself.
https://www.reddit.com/r/business/comments/3pcnlh/what_the_n...