Washington, D.C. ? FBI officials attempted to bolster their case against researcher Bruce E. Ivins on Monday by presenting experts who said that a lone scientist working for three to seven days with readily available equipment could have produced the lethal spores used in the 2001 anthrax mailings.

Investigators reverse-engineered the deadly material sent to Senate offices and media organizations and concluded that a single person could have manufactured and dried it, said James P. Burans, director of the National Bioforensics Analysis Center.

Yet bureau officials and scientific experts acknowledged that they have not resolved all of the intricacies of the bacterial powder that killed five people, injured 17 others and set off a national panic after it showed up in the U.S. mail at various locations along the East Coast after the Sept. 11 attacks.