Complex sentence: The authorities never proved the perpetrators of the crime were Marjorie and her husband, though they had substantial evidence to do so, including a letter and a ring of Elisabeth's that Marjorie was found wearing after her mother's death.
Split into simpler sentences: The authorities never proved the guilt of Marjorie and her husband, though they had substantial reason to do so. Evidence included a letter and a ring of Elisabeth's that Marjorie was found wearing after her mother's death.