WASHINGTON — The Federal Bureau of Investigation on Wednesday outlined a pattern of bizarre and deceptive conduct by Bruce E. Ivins, an Army microbiologist who killed himself last week, presenting a sweeping but circumstantial case that he was solely responsible for mailing the deadly anthrax letters that killed five people in 2001. After nearly seven years of a troubled investigation, officials of the F.B.I. and the Justice Department declared that the case had been solved. Jeffrey A. Taylor, the United States attorney for the District of Columbia, said the authorities believed “that based on the evidence we had collected, we...