The Dead Sea Scrolls demonstrate Christianity was only one of several branches of Judaism which was expecting a Messiah.  The DSS show the Qumran community expected the Messiah to be "pierced" or crucified and then rise from the dead.  The Qumran community also believed in "ritual cleansing" which Christians would see as baptism.  For Latter-day Saints, the DSS show Joseph Smith's descriptions of ancient records stored in the ground to come forth in the future was accurate.  That is precisely what the DSS are as well.