They've done the DNA tests, both with previous samples, and with samples taken from his sons, and they're definite its him. As to the shrouding it in mystery, when you're trying to capture someone as elusive as Saddam is, you don't announce your movements, you keep it quiet until at least a day after the capture; that way they can't defend or alternatively rescue him. They're going to put him on trial (supposedly by Iraqi people in the jury and deciding his sentence) in the new year.
This is a very good day for the people of Iraq, and I wish them the best, and the peace, stability and tolerance that they so deserve.