tomorrow night on "48 hours mystery," erin moriarty reveals new evidence in shannon gilbert's death. e could be killing someone as we speak. >> reporter: sheri's sister shannon, an escort on a call, went missing from a gated community just three miles from the dumping ground of the long island serial killer. in may of 2010. it was the search for shannon that led to the four victims -- young women like shannon, all linked to the sex trade. >> this is the american version of jack the ripper. that's the kind of case that this is. >> reporter: on the last night of her life, shannon made a 911 call pleading for help, ran from her client's home and disappeared into the night. police finally found her body 18 months later in a nearby marsh. >> we have located the skeletal remains. >> reporter: richard dormer who was police commissioner at the time told "48 hours" he shannon's death was not related to the serial killer. he believes she ran into the marsh, disoriented and drowned accidentally. but then why were her clothes found a quarter mile away. >> that's explainable but she's hysterical a