On Friday, the FBI and Justice Department officially closed their probe into the 2001 mailing of letters laced with anthrax to Capitol Hill and journalists across New York and Florida, after concluding that Bruce E. Ivins, the US Army medical researchers, was the only one responsible for the 5 deaths that happened as a result.

Had Ivins not taken his own life in July of 2008 with the investigators closing in on him, he would have been most probably slapped with charges of using a weapon of mass destruction, as has been revealed by the authorities in their report on the case and its official closing.

The announcement of the closing of the case was accompanied by the revelation of various supporting documents, which included over a thousand pages of summaries, e-mails, search warrants and other evidentiary material.

The FBI, in association with postal inspectors and federal prosecutors, reached the conclusion that Ivins had various opportunities to create and maintain the spore batches of the virus anthrax.

"In addition, Dr. Ivins was among the very few anthrax researchers nationwide with the knowledge and ability to create the highly purified spores used in the mailings", the report said, while stressing that his motive was born out of "intense personal and professional pressure”.