Doubly and triply excited states of three-electron systems provide the case for a highly correlated fourbody Coulomb problem. We have developed a sophisticated three-electron Configuration Interaction (CI) code based on explicitely correlated Hylleraas (Hy) functions for arbitrary total angular momentum and spin, which has been implemented with an uniform complex scaling (UCS) method to deal with resonant states. At present, this UCS-HyCI tool allows us to perform computations to uncover resonant states of the Helium negative ion, with the highest accuracy possible.