"48 Hours" uncovers missing escort Shannan Gilbert's final minutes

New information on the death of missing escort; Search for Gilbert led to discovery of serial killer's graveyard on Long Island

Produced by Clare Friedland and Liza Finley

(CBS) OAK BEACH, Long Island -- Since late 2010, 11 bodies -- nearly all young woman, have been found along a stretch of beach on New York's Long Island. So far, there has been no arrest, but since our last "48 Hours" broadcast, there are new developments in the case. And more questions about a curious character who put himself right in the middle of the mystery.

In the hours after midnight on May 1, 2010, Shannan Gilbert, an escort on her way to a job, drove past the place where the bones of the Long Island Serial Killer's victims lay hidden in the brush. She didn't know it then, but the mysterious events of the next few hours would forever link her to four young women - whose bodies were found wrapped in burlap -- and spark one of the largest murder investigations in Long Island history. And so it began.

"My sister was last seen running along the roads ... She felt like she was in fear for her life that night," Sherre Gilbert told "48 Hours" correspondent Erin Moriarty. "She just disappeared into the night."

It would be two days before Sherre learned her sister was missing ... when Shannan's worried boyfriend called to say she hadn't come home.

"Immediately, I started to panic," she said. "I could hear the fear in his voice."

It was the call Sherre and her sister, Sarra, had been dreading ever since learning Shannan, diagnosed with a bipolar disorder and struggling with depression and mood swings, had turned to selling her services online as an escort.

"What would she tell you when you would say you were worried about it?" Moriarty asked Sarra.

"She pretty much thought that, you know, it would never happen to her," she replied.

The Gilberts say they immediately filed a missing persons report, but with no news, they drove 140 miles from their home in upstate New York to Oak Beach, Long Island, to look for Shannan themselves. By then, she had been missing for eight days.

"We went to all the houses around the area to, like, knock on their doors and just say, 'Hey listen, did you see my sister?'" Sherre said. "We gave them flyers. We went everywhere."

They spoke to a dozen witnesses and homeowners in the area trying to piece together a timeline. They learned that Shannan and her driver had left New York City shortly after midnight on May 1, 2010, and headed to a gated community in Oak Beach.

"My sister met the client through Craigslist and went to his house around 2:00 a.m.," Sherre explained. "Her driver dropped her off and she was there for quite a while and then ... for some reason, she started to panic."

Shannan's sister believes something awful happened in that house to terrify her because of a 911 call Shannan made from right inside the client's home. It was 4:51 a.m.

Former Suffolk County Chief of Detectives Dominick Varrone, who has heard the call, is speaking for the first time on network television.

"She's saying, 'There's someone after me; there's someone after me,'" he said. "It's a girl who clearly believes ... she's in harm's way."

"Does she say who she's afraid of," Moriarty asked Chief Varrone.

"She just says 'they're trying to kill me,'" he replied.

Varrone says two male voices are recognizable in the background: Shannan's driver and the man who hired her, Joseph Brewer. As Brewer is heard trying to get her to leave his house, Varrone says, "He either approaches her or touches her and ... you hear her scream out."

But police couldn't respond to the call because Shannan couldn't say where she was.

"The complaint operator's asking, 'Well, where are you?' And she just kind of ignores that 'where are you' question and keeps saying 'someone's after me,'" Varonne explained. "She sounds ... not very coherent, not very rational."

"But wouldn't you sound that way if you were panicked and afraid?" Moriarty asked Varrone.

"You could make that argument," he replied. "It almost seems like she's in some type of psychotic state or in some type of drug-induced stupor."

Still on the 911 call, Shannan fled the house ... running towards the nearby home of Gus Colletti, a retired insurance fraud investigator and resident of Oak Beach for over 30 years.

"It was like 5:00 in the morning," Colletti recalled. "I was in the bathroom shaving. ... All of a sudden, I heard screaming out here and banging on that door. Yelling, 'Help me, help me, help me.'"

He opened the door. "And I said to her ... 'What's the matter?' She wouldn't answer me. She just kept staring at me and going, 'Help me, help me, help me.'"

"This is all on the audiotape," Varrone said. "We hear the conversation between the two of them ... and she's just staring at him and not acting rationally."

"I reached over and grabbed that phone, dialed 911," Colletti continued. "When I said to her, 'I called the police. Sit down in that chair. They're on their way,' She just looked at me and she ran right out the door."

Colletti said it was then that he noticed an Asian man in his 30s driving a black SUV. It was Michael Pak, Shannan's driver.

"I could see a car come and stopping, coming a little bit and stopping," he said.

Asked if he thought Shannan was afraid of the man in the SUV, Colletti

replied, "She was afraid of somebody."

Then, Colletti saw Shannan was hiding underneath the boat in his yard.

"All of a sudden, she took off, out from under the boat ... and he took off after her. And I yelled to him to stop. And he didn't and he followed her around that way," he said.

At that point, Colletti called 911. It was now 5:21 am. Shannan ran towards the home of another Oak Beach resident, Barbara Brennan.

"We know she's alive 'cause she's banging on Mrs. Brennan's door ... and Mrs. Brennan calls 911," said Varrone.

But when police arrived at 5:40 a.m., Shannan Gilbert had vanished. They assumed she had already left the area with her driver, Michael Pak.

"All the responding officers can believe at this point is that whoever was in the SUV picked up this girl and they're gone," said Varrone.

Chief Varrone says the local police responding to Colletti's call knew nothing about Shannan's own 23-minute 911 call. What has never been reported before is that Shannan's call was transferred to the New York State Police when she couldn't tell them where she was. It took nearly a month for police to connect Shannan's desperate call to the missing persons report her family had filed in New Jersey, where Shannan lived.

"If Michael Pak had stayed there and told the officers that she was still missing, is it possible that Shannan Gilbert might still be alive?" Moriarty asked Varrone.

"It's possible," he replied. "He may have looked for her as he was driving out the gate ... but he certainly was nowhere to be found when officers responded and arrived."

Sherre Gilbert says her sister was desperately trying to make a better life for herself.

"My sister had other dreams, you know. She wanted to be a singer, an actress. She was pursuing that. And she was also goin' to school to be a writer," she said.

No one knew then, that seven months later, the search for Shannan would turn up the grisly grave site of the bodies of four other young women who, just like Shannan, had simply disappeared.

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