After facing people’s doubts about the way they handled scientist Bruce Ivins’ case, the FBI held a two-hour briefing conference on Monday at the agency’s headquarters, revealing some of the probe’s mysteries. At the same time, they also acknowledged that they may never be able to satisfy everyone with their findings.

“I don’t think we’re ever going to put the suspicions to bed. There’s always going to be a spore on a grassy knoll,” Vahid Majidi, head of the FBI’s weapons of mass destruction division.

Ivins committed suicide last month by taking a massive dose of Tylenol mixed with codeine just as the Justice Department was preparing an indictment against him. Since then, many have questioned the FBI probe and Ivins’ implication in the 2001 anthrax attack, which killed five people, injured 20 others and crippled the US’s mail system.

“I think it's going to be one of the great conspiracy theories, like whether we landed on the moon or whether Lee Harvey Oswald acted alone,” in assassinating President Kennedy, Edward Lake, a computer specialist from Wisconsin whose Web Site has kept people in touch with the anthrax attacks for years.

At the conference, officials said that only eight of more than 1,000 anthrax samples collected by the FBI in the years after the attack have the same makeup and all eight can be linked back to Ivins’ flask. Also, 100 scientists had access to these samples and all of them were investigated. The “body of evidence” pointed to Dr. Ivins, officials said.

However, an analysis on a hair sample recovered from a mailbox in Princeton made by FBI experts themselves and the US Postal Service inspectors revealed that the hair doesn’t match the lead prime suspect casting more doubts on the case.