~~Yes they do. This act falls under the purview of civilian enforcement. It is up to the controlling government to prosecute these civilian crimes in civilian criminal court.~~

EDIT: Okay, so this particular argument irked me so I investigated. Unfortunately, Ninja is technically correct. According to the ICRC civilians receive an instantaneous removal of their status as non-combatant for the duration of the hostile act, and the ICC's Rome Statutes clearly list using poison as a warcrime so it is probable the perpetrators could be prosecuted. More likely, however, is that their being subject to civilians laws means they can ALSO be prosecuted in the civilian manner. Double the risk for the reward.

That said. Russia wants to FAFO that's their problem.