The physical properties of oxide heterointerfaces depend crucially on the electronic and ionic reconstructions across the interface. For the formation of a two-dimensional electron liquid (2DEL) at the interface of LaAlO₃/SrTiO₃ (LAO/STO) systems, although it is well accepted that the conduction of amorphous-LAO/STO samples comes exclusively from the oxygen vacancies due to interfacial redox reactions, the relative contribution of ionic reconstruction and electronic reconstruction to the conduction at the polar crystalline LAO/STO interface has been a topic of debate. Herein, by resonant x-ray photoemission spectroscopy and x-ray absorption spectroscopy measurements, we investigated the evolution of the Ti 2p signal as well as the in-gap states at the diluted oxide interface of LaAl_1−xMn_xO₃/STO (0≤x≤0.3), where the doping of Mn into LAO gradually decreases the carrier density of the interfacial 2DEL but does not change the interface polarity. The spectroscopic results present direct evidence that the conduction from redox reaction at polar LAO/STO interfaces is suppressed by increasing the Mn doping level without the need of oxygen postannealing. A pure polarity discontinuity induced electronic reconstruction can be achieved by deliberately controlling the Mn doping level in LAO, which results in low-carrier, high-mobility, and spin-polarized 2DELs at x=0.3.