Final answer:
The white powder contained the anthrax bacterium, causing deaths and illnesses. Anthrax is caused by the introduction of endospores from the bacterium Bacillus anthracis into the body.
Step-by-step explanation:
The white powder that was sent through the US Mail and caused several deaths and illnesses was containing the anthrax bacterium. In 2001, letters containing anthrax spores were mailed to news offices and U.S. Senate offices, resulting in 22 infections and 5 deaths. Anthrax is a disease caused by the introduction of endospores from the bacterium Bacillus anthracis into the body.