THE FAMILY OF SHANNAN GILBERT BELIEVES SHE COULD BE THE VICTIM OF A LONG ISLAND SERIAL KILLER AND THEIR ATTORNEY CHALLENGES THE POLICE THEORY ABOUT HER DEATH "LONG ISLAND SERIAL KILLER" SATURDAY, JUNE 23 (10:00 PM, ET/PT)

Police suggest Shannan Gilbert died in a Long Island marsh after becoming disoriented and frantically running toward the lights of a highway. Her family says she was murdered and dumped near where 10 other bodies were found, perhaps the victim of a serial killer. Now on 48 HOURS MYSTERY, the family and their attorney challenge the official theory of what happened to Gilbert on an updated edition of "Long Island Serial Killer" to be broadcast Saturday, June 23 (10:00 PM, ET/PT) on the CBS Television Network.

"The perfect place to have put her body if you murdered her is exactly where she was found," Gilbert family attorney John Ray tells 48 HOURS MYSTERY correspondent Erin Moriarty.

Shannan Gilbert's disappearance occurred during the killing time for the alleged Long Island Serial Killer, who has dumped his victims along a secluded beach on Long Island, N.Y. When Gilbert went missing in May 2010, the search for her led to a serial killer's graveyard. Ten bodies were found and the killer is still out there.

Police have refused to count Gilbert among the victims, though her family's attorney says the similarities can't be ignored. Gilbert was an escort on her way to a job in the Oak Beach area in the hours after midnight on May 1, 2010. However, before Gilbert disappeared, she spent 23 minutes on the phone with a 911 operator, reportedly insisting someone was going to kill her.

Police didn't find her that night. The search continued for more than a year, during the course of which they found the bodies of 10 others. Finally, in December 2011, they located Gilbert's skeletal remains, separated by a quarter mile from her jeans, shoes and other personal items. Richard Dormer, then Suffolk County Police Commissioner, theorized Shannan was disoriented, shed her belongings while running into the swamp, and drowned or died of exposure.

John Ray disagrees, and to prove his point retraced Gilbert's trail through the marsh on this edition of 48 HOURS MYSTERY. "There isn't a scintilla of a reason why she would take off her jeans, leave them behind to run half-naked into the swamp," Ray tells Moriarty.

Ray suggests she was murdered elsewhere and dumped at the beach. "You'd want to put the body deep enough into the marsh from the parkway that children, pedestrians would not find her," he explains.

Sherre Gilbert insists her sister was murdered. "You never know. He could be out there killing innocent women," she says.

Police say the investigation into the Long Island Serial Killer continues and the Shannan Gilbert case remains open.

This broadcast is produced by Liza Finley, Gregory F. McLaughlin, Lincoln Farr and Taigi Smith. Judy Tygard is the senior producer. Al Briganti is the executive editor. Susan Zirinsky is the senior executive producer.