The phenomenon of holographic light scattering in centrosymmetric crystals of sodiumnitroprusside is investigated by analyzing (1) the effect of light polarization and wavelength of pump- and readout beams, (2) the angular intensity distribution and (3) the kinetics of scattered light. It is shown, that the scattering phenomenon and the corresponding properties can be entirely explained by diffraction processes of the pump beam from parasitically recorded slanted phase gratings without assuming any beam-coupling processes. The kinetics originates from the nonlinear photorefractive recording mechanism. Further we present a new approach for three-wave interaction including diffraction processes at higher harmonics, that explains the temporal build-up of wide-angle scattering in media with a nonlinear photorefractive response.