An F.B.I. briefing on Monday was supposed to bolster the agency’s conclusion that a lone, disturbed bioterrorism scientist was responsible for the 2001 anthrax attacks that killed five people, sickened 17 others and terrified the country. It fell short of its goal.

The F.B.I. spent years pointing a finger at a different suspect. It is not enough for the agency to brush off continuing skepticism. “There’s always going to be a spore on a grassy knoll,” Vahid Majidi, the chief of the agency’s weapons of mass destruction division told reporters.

A group of independent experts needs to look hard at the F.B.I.’s technical analysis and detective work that combined to convince investigators that the mailed anthrax must have come from Dr. Bruce Ivins, a scientist at the Army’s bioterrorism lab in Fort Detrick in Maryland.

The core of the F.B.I.’s case, was the use of new microbial forensic techniques to match the mailed anthrax with anthrax that the agency says was prepared by Dr. Ivins and contained in a flask that he controlled. Experts identified four distinct genetic markers among the anthrax spores in the mailings. They analyzed anthrax samples gathered from laboratories around the world. Ultimately, they concluded that only anthrax batches prepared by Dr. Ivins contained all four mutations.