Complex sentence: They were identified as Pete Spence (an alias for Elliot Larkin Ferguson) and Frank Stilwell, a business partner of Spence who had shortly before been fired as a deputy of Sheriff Behan's (for county tax "accounting irregularities").
Split into simpler sentences: They were identified as Deputy Sheriff Pete Spence (an alias for Elliot Larkin Ferguson) and Deputy Sheriff Frank Stilwell, a business partner of Spence. Stilwell was fired a short while later as a Deputy Sheriff for Sheriff Behan (for county tax "accounting irregularities").