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We have made high-accuracy measurements of the integrated Stokes parameters for resonance fluorescence from polarized electron-impact excitation of the 4p55p[5/2] 3D3 and 4p55p [5/2] 3D2 states of Kr. We report measurements in the region within 0.6 eV of threshold, which is below the first cascade threshold. We also present theoretical calculations of these Stokes parameters using a recently developed relativistic Breit-Pauli Rmatrix code. In well LS-coupled systems, nonzero values of the integrated Stokes parameter P2 signal relativistic effects (like continuum spin-orbit coupling, i.e., Mott scattering). A single value of P2=4(4)310-3 at 12.0 eV was previously reported in this energy range [Furst et al., Phys. Rev. A 47, 3775 (1993)]. We have now measured P2 at six different energies in this region to comparable precision. These results are consistent with P2=0 and with the theory. We discuss the effect of the electron-beam energy width on the accuracy of the measurements. Even when such effects are accounted for, serious discrepancies remain between theoretical and experimental results for excitation of the intermediately coupled 3D2 state.