Washington ? The FBI is closely scrutinizing 20 to 30 scientists nationwide for possible connections to last fall’s deadly anthrax attacks, including a biodefense researcher whose home and storage facility were searched this week, a U.S. government official said Thursday.

The FBI has a special interest in Dr. Steven J. Hatfill, whose apartment and storage facility were searched, based solely on his past interest in bio-terrorism and his access to anthrax, said the official, who spoke on the condition of anonymity.

Hatfill is a “person of interest” a group that includes 20 to 30 researchers nationwide whose expertise and access might have given them the knowledge and opportunity to send the deadly anthrax letters, the official said.

The homes of some of the other researchers also have been searched, said a federal law-enforcement official, who also spoke on condition of anonymity.

Investigators believe anyone skillful enough to send the anthrax letters without becoming sick must have had extensive experience with the deadly substance, the official said.

Yet, despite having focused on scientists, the FBI still believes the attacker may not be associated with anthrax research, the official said.

Hatfill commissioned a 1999 study depicting a hypothetical anthrax attack by mail while working for defense contractor Science Applications International Corp., said Ben Haddad, spokesman for the San Diego-based company.

The study was written by bioterrorism expert William C. Patrick III and described placing 2.5 grams of Bacillus globigii, a simulated form of anthrax, in a standard business envelope, The (Baltimore) Sun reported.

The newspaper said portions of the study were read to it by a person who has a copy.

Hatfill, 48, is listed as a 1983 graduate on the Web site for the University of Zimbabwe Medical School, and he provided to the school his e-mail address from SAIC. Investigators also have confirmed that Hatfill was a graduate of the school.

The university is near the Greendale neighborhood of the capital Harare. “Greendale School” in Franklin Park, N.J., was printed in large block letters as the false return address on the anthrax-laden envelopes sent to Sens. Tom Daschle and Patrick Leahy.

One investigator cautioned that the FBI has been unable to place Hatfill near Trenton, N.J., during the time the anthrax letters were mailed. Officials are convinced those letters were mailed from the Trenton area.

In Florida, meanwhile, FBI agents on Wednesday also searched a storage facility in Ocala used by Hatfill.

Hatfill has denied involvement in the anthrax mailings.

Five people died in the anthrax attacks that began in late September.