Who says Russia wants to kill them? Maybe it just wants to render them ineffective. That has been achieved ("Others have suffered such severe long-term cognitive and vestibular aftereffects that they can no longer function on a day-to-day basis and have been medically retired from government service.").

I think it's sensible to suspend judgment for now, but this is clearly one of the two main plausible contenders for an explanation of the observed phenomena.