In practical terms, there REALLY should be an agreement between NATO countries as to how to discourage RUS spies & saboteurs. As it stands, they do horrible things, get exchanged - often for innocent people - then become national heroes.
At minimum, their possessions and all funds in their available accounts should be seized, and they should be tried and required to confess & cooperate first - in a way that would embarrass Russia and Putin - as a precondition to EVER being traded.