I don't usually link to blogs, but this is especially good:
http://www.talkingpointsmemo.com/archives/week_2003_12_28.html#002356. . .
But there's another possibility: that is, that this decision isn't the result of the general progress of the investigation or the accumulation of evidence, but something specific. Or more to the point, a specific person. And that something has just taken place.
Obviously these are general scenarios, which may, in reality, overlap quite a bit. But what strikes me about this announcement today was its timing. And the timing leads me to think the third scenario is the most likely.
. . .