I don't see a veritable admission of guilt. I see an investigator whose suspect was identified too early to suit him, making a circus of the investigation. I haven't seen any evidence (that word) that the FBI has given up its belief that Steve Hatfill is behind, or at least connected to, the 2001 anthrax letters. I haven't seen any sign that they are looking at (or that they ever>looked at) anyone else.
The FBI is in a tough position. They seem to believe that Hatfill did it, but despite huge expenditures, they not only can't prove it, they don't seem to be able to indict him at this time (lawyers have a saying that you can indict a tree... a prosecutor has a lot of leeway before a grand jury that he won't have in a courtroom).
Steve Hatfill is also in a tough position. Only he knows if he did it, or not. If he did not, he has no way of proving to the FBI he didn't do it, and if his attorney is not a complete bozo, he has advised Hatfill not to talk to them. Especially given the FBIs policy to never record interrogations, he would be taking a gargantuan risk with no upside -- whether he was innocent or not.
The FBIs investigatory process depends 100% on the absolute integrity of the Special Agents and support staff involved. Unfortunately, many recent cases (Hanssen, Connolly, etc). indicate that we can not rely 100% on this at all. Their methods are fraught with opportunities for abuse. Even though the overwhelming majority of FBI agents work diligently within our laws and Constitution for the good of our nation, we can't assume that that is the case: somebody needs to watch the watchers.
d.o.l.
Criminal Number 18F
I'm not sure if Hatfill is still being tailed 24-7 or not, but this article tells me that the anthrax case is pretty close to slowly fading away to Jack the Ripper status.