Measurements of the spin polarization of photoelectrons in the autoionization region of the Hg 6s2-subshell using circularly polarized synchrotron radiation and using unpolarized light from rare gas discharge lamps are reported. The results obtained show a pronounced structure across the resonances. Together with data of the cross section and its angular distribution these data from a complete parameter set for the determination of the transition matrix elements and the phase difference of the continuum wavefunctions. Evidences for strong configuration interaction and channel mixing between the open and closed channels were found. The matrix elements and their ratio vary strongly across the resonances and the relative phase shows some changes of sign. A change of the relative phase by Pi across an autoionization resonance, predicted by Fano, has been verified experimentally for the triplet resonance. We would like to express our gratitude to Professors W. Paul, G. Nöldeke and J. Kessler for their continued interest and encouragement. We thank Dr. D. Husmann, Dr. J. Hormes and B. Osterheld for their assistance in performing the experiment in Bonn. We are grateful to Dr. N.A. Cherepkov for helpful discussions and acknowledge support by the DFG and BMFT.