Nonsense about analogy with DNA. "Jihadmobils" used by ISIS are based on Toyota SUV and belonged to somebody before they were taken by terrorists. So, blame the previous hosts they were stolen from, or Toyota?
In the chaos that was in Syria in 2013 (and still is), various groups or rebels and terrorists could capture the governmentals stocks and use it later.
When the US destroyed one of the Assad's AF base about a year ago, the explanation was that chem. weapons were there. But when the US were invited to visit it after and collect whatever samples they would find, they refused.