Didn't they poison some guy with radioactive isotopes a few years back? I don't think they care about it being attributed to them, or think that being attributed to them has positive value.
I recall that the [very small] quantity of Polonium-210 involved had a market value of $20 Million and was tied directly back to the state atomic agency requiring the personal authorisation of the Commander-in-Chief. So a rather extravagant and blatant way of dispatching someone (with curiously bungling assassins).
https://www.google.com/search?q=alexander+litvinenko