I totally suspect the three BA Miami->London deaths to be something like ricin.
We heard Houston cops talk about balloons..
The Kabul office of Pakistani scientist Mehmood is reportedly found to contain documents indicating an interest in anthrax, including calculations concerning the aerial dispersal of anthrax via balloon, and an Associated Press photo showed something at the anthrax vaccine laboratory described as "anthrax spore concentrate"
And, here's the Ricin connection..............
Ansar al-Islam is reported to have been experimenting with ricin, a deadly toxin, including on at least one human being. This report is denied by Ansar spokesman Muhammad Hasan Muhammad
http://cns.miis.edu/pubs/other/sjm_cht.htm