Some questions and answers about the latest developments in the federal investigation of the anthrax attacks:

Q: Are we any closer to knowing who sent anthrax-tainted letters through the mail last fall?

A: Not really. Seven months after the first anthrax-tainted letters were discovered, investigators remain frustrated in efforts to find the anthrax mailer. Using traditional methods, the FBI has interviewed hundreds of people who currently or previously worked for U.S. labs with access to anthrax or contractors who worked on the U.S. anthrax programs. Some of the dozens of people the FBI initially focused on have passed lie-detector tests. Many are now being interviewed again. Forensic testing on the envelopes has not turned up much, such as fingerprints or saliva residue, because investigators believe the anthrax-mailer took careful precautions not to infect himself; for example, the envelopes used pre-affixed stamps.

Q: What kind of scientific testing is being done?

A: Some top civilian scientists are working with the FBI to compare the genetic structure of the mailed anthrax with samples from the nation's scientific laboratories, in efforts to pinpoint or exclude labs as the possible origin. But this type of study is unprecedented, and it is unclear to the FBI whether the results will be useful or even allowed by a judge as evidence in a criminal trial. "We have an ongoing, very thorough laboratory investigation undertaken,'' FBI Director Robert Mueller said.

Q: What type of person does the FBI believe did this?

A: Early in the investigation, the FBI decided the anthrax-mailer was most likely a domestic terrorist, a single person with experience working in a scientific lab. This person was described as having a "clear, rational thought process and appears to be very organized in the production and mailing of these letters.'' The FBI said the mailer probably has or had legitimate access to biological agents in a lab, and probably was "standoffish,'' preferring to work alone rather than in groups. But investigators are now beginning to reconsider some of those assumptions, including whether the anthrax-mailer was in the United States, though the FBI is not throwing out its profile. "No one is ruling out anything,'' one investigator said. Mueller told a Senate panel last week: "The profile that we came out with then was based on certain information that we had at that time. The results of additional interviews, the results of the tests that we have done to date -- many of them are preliminary -- has not warranted at this time a revision of that profile.''

Q: What is the death toll?

A: Five people died from inhaled anthrax and at least 13 others were infected with other forms of the disease.