Short answers, pulled from the story.
The first documented instance of biological warfare dates back to the years between 1500 and 1200 BC. Hittite texts recorded a strategy of driving victims of an unknown plague into enemy lands to trigger an epidemic.
During the siege of Kaffa in 1346, Mongol forces of the Golden Horde catapulted the corpses of warriors who had died of plague over the city walls. This move may have resulted in the deaths of approximately 25 million Europeans and linked the event to the spread of the Black Death.
Unit 731 was a secret Imperial Japanese Army unit commanded by Lieutenant General Shirō Ishii. The unit conducted horrific human experiments and deployed biological weapons against Chinese civilians and soldiers.
The Biological Weapons Convention entered into force on the 26th of March 1975. This followed the decision by US President Richard Nixon to unilaterally terminate the American offensive biological weapons program in 1969.
The cost of a biological weapon is estimated to be only 0.05 percent of the cost of a conventional weapon. This low cost makes it an attractive option for terrorist organizations like Al-Qaeda.
The incubation period of biological agents typically lasts 3 to 7 days. This timeframe provides terrorists with a window to escape before government agencies can respond to an attack.