What did the FBI conclude about the person responsible for the 2001 anthrax letter attacks?

In early 2010, the Federal Bureau of Investigation concluded its investigation into the 2001 anthrax letter attacks. The agency determined that the letters were mailed by a microbiologist who had worked for years within the U.S. Army’s biological defense program. The individual, who had been named a suspect in the case, committed suicide in 2008.1