Remember, the Aum Shinrikyo cult in Japan managed to make Sarin (GB) nerve gas in a home chemical lab before their attack in 1995. Tabun (GA) is likely easily made in a home chemical lab, and its lethality is almost as bad as Sarin. Imagine an ISIS or ISIS-inspired terrorist putting Tabun in a pressurized container and then releasing it in a crowded shopping mall or train station; unless the victim is given atropine as an antidote quickly, one whiff of Tabun will kill a person within 15 minutes in a most excruciating manner.
And remember, just days ago, guys were caught crossing the Border with empty stainless steel containers.