Hunt for the Long Island Serial Killer: How Escort Shannan Gilbert's Disappearance Led Police to a Graveyard

The bodies of at least 10 victims have been found on New York’s Gilgo Beach. Are they connected? Subscribe to PEOPLE now for details of the Long Island Serial Killer, on newsstands Friday.

In December 2010, a police officer and his dog went out on Gilgo Beach on Long Island, New York, searching for missing 24-year-old Shannan Gilbert. They found a woman’s body wrapped in burlap — but it wasn’t Shannan.

Over the next several days, police discovered three more young women, all within about 500 feet of one another and all wrapped in burlap.

They kept finding bodies: Six more sets of remains were discovered in the early part of 2011 until, finally, Shannan’s partially clothed body was found hidden deep in the overgrown Gilgo Beach brush.

“The first body we found we presumed was Shannan Gilbert,” Suffolk County Police Chief Stuart Cameron tells PEOPLE in this week’s issue, on newsstands Friday. “Then we found a second body, a third, a fourth … The shock set in.”

Now, Suffolk police say they are desperate to solve “one of the most high-profile cases” in their history, dubbed the Long Island Serial Killer. But many puzzles remain: Were all the victims killed by the same person? What connects them? And how many are there?

• Watch our new 10-part true crime show, People Magazine Investigates, which debuts with the two-hour season premiere “The Long Island Serial Killer” on Monday, Nov. 7, at 9 p.m. ET on Investigation Discovery

Authorities tell PEOPLE they believe at least the first four victims are connected — all had been in contact with their killer through online ads and via their cell phones — but police are looking at all victims found in the area as far back as 1996.

WATCH: People Magazine Investigates Series Premiere Trailer: Long Island Serial Killer

And while the first four victims were all strangled and wrapped in burlap, three others had been dismembered, their causes of death unclear. A toddler is also among the dead, as is an unidentified Asian man wearing women’s clothes, who was brutally beaten.

“We can’t say beyond a shadow of a doubt all these murders are connected,” says serial-killer profiler and expert John Kelly. “But serial killers can change their [methods]. A sadistic killer would be about convenience.”

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Lynn Barthelemy’s 24-year-old daughter Melissa was among the women first found in burlap six years ago. She tells PEOPLE in this week’s issue how painful it is to revisit Melissa’s killing — and how necessary.

Lynn says, “I keep talking about her in hopes it will help solve her murder.”