Dorothy Salisbury Davis's "Backward, Turn Backward" (1960).

In this January 31, 1960, episode from Alfred Hitchcock Presents, a sheriff looks into the seemingly iron-clad case of murder against a man who had been romancing a much younger woman. It's based on the June 1954 EQMM story "Backward, Turn Backward" by MWA Grand Master and Edgar nominee Dorothy Salisbury Davis, now age 96.