The potential may be there but how are you going to do this. The worst biological agent was probably the pandemic of 1918. Maybe Aids is similar. Chemical agents that I know off need a delivery system.
The Archeology War
At the invitation of the Pentagon, archaeologists have provided military planners with the locations of hundreds of Iraq's outstanding ruins from antiquity. But the entire country, experts say, is an archaeological site. http://www.nytimes.com/2003/02/25/arts/design/25DIG.html