In the week since the government's top suspect in the 2001 anthrax attacks committed suicide, a sometimes bizarre portrait of 62-year-old Army scientist Bruce Ivins has emerged. But while Ivins had access to the deadly toxin and his therapist's portrayal of him is haunting, there are a number of unanswered questions in the FBI's case against Ivins.

Some may be answered when the Justice Department unseals key documents detailing its evidence against Ivins. Others will remain unanswered, adding more uncertainty to an already mysterious case.

Below are some of the biggest unanswered questions in the "Amerithrax" case and the possible answers that have emerged so far.

Q: How could Ivins get access to powdered anthrax, since the biological warfare lab at Ft. Detrick did not deal with the toxin in that form?

A: There is no indication that authorities can prove Ivins made the powdered form of bacteria. Investigators say that in 2001, Ivins borrowed a device, known as a lyopholizer, capable of converting anthrax spores into powder. But some colleagues say it would have been difficult, if not impossible, for Ivins to do that unnoticed.

Q: How can the FBI link Ivins to the anthrax for certain?

A: The FBI used advanced DNA testing to track the anthrax that killed five people to a sample Ivins controlled, but as many as 12 others had access to it. It's unclear for now exactly how the FBI eliminated those others as suspects.

Q: What motive would Ivins have had to unleash an attack?

A: One investigative theory is that Ivins released the toxin as a way to test cures he was developing or a vaccine he had recently patented. But it's unclear whether the FBI can prove that. Ivins' therapist said the scientist had a history of homicidal and sociopath tendencies, but his friends say his mental deterioration was caused by the FBI's relentless pursuit.

Q: Did Ivins travel to Princeton, N.J., where the anthrax letters are believed to have been mailed?

A: Authorities cannot place Ivins in Princeton when the letters were mailed. And the only explanation for why he'd make the seven-hour round trip is bizarre. Authorities say Ivins was obsessed with the sorority Kappa Kappa Gamma, dating back to his own college days. The Princeton mailbox is not far from the school's sorority office , and authorities say Ivins had made unexpected visits to the sorority at other schools .

Q: Why target media organizations and politicians?

A: The FBI's initial behavior analysis said it's unlikely that NBC News, the New York Post and then-Sen. Tom Daschle were selected randomly. Analysts said the targets are probably very important to the offender and may have been the focus of his contempt. There is no indication, for now at least, that Ivins demonstrated such feelings. Under the theory that Ivins was testing his cure, lawmakers and media might drum up attention for the importance of anthrax drugs, but it's unclear whether there's any evidence about that.

Q: Has the FBI matched handwriting samples from the letters?

A: FBI handwriting analysts described a distinct writing style on the envelopes and letters sent along with the anthrax. The letters were all capitalized and block-style. The names and addresses tilted downward from left to right. The word cannot was written as can not. The numeral one was written quite formally. The writer selected dashes instead of slashes in the date 09-11-01. The FBI has seized numerous documents in the case but it's unclear whether the handwriting has been matched.