The interplay between the LHC and the $e^+ e^-$ International Linear Collider (ILC) with $sqrt{s}=500$ GeV might be crucial for the discrimination between the minimal and next-to-minimal supersymmetric standard model. We present an NMSSM scenario, where the light neutralinos have a significant singlino component, that cannot be distinguished from the MSSM by cross sections and mass measurements. Mass and mixing state predictions for the heavier neutralinos from the ILC analysis at different energy stages and comparison with observation at the LHC, lead to clear identification of the particle character and identify the underlying supersymmetric model.