Long Island Murder Mystery: Everything We Know About the Gilgo Beach Case Thus Far

It's been more than five years since New York police discovered a mass grave at New York's Gilgo Beach in 2011. But the recent death of the motherof one of the deceased has brought the years-old case back into national headlines and the suspected Long Island serial killer back into the minds of many.

The mother of Shannan Gilbert, the sex worker whose body was found near the mass grave, was found dead suffering stab wounds on Saturday. The woman's other daughter, Sarra, was charged with her murder.

A missing-person's specialist said the family "never found closure" after Shannan's death, and that may have played a role in the recent tragedy.

"When your loved one is missing, the torture is too much for family members," Dottie Laster told PEOPLE amid revelations that Sarra suffered from schizophrenia. "Over time, they can develop serious medical malfunctions."

Here's everything we know about the Long Island murder mystery:

Shannan's Death is Not Connected to the "Serial Killer" Case

Shannan, a 24-year-old from New Jersey, disappeared in May 2010 after meeting a client through Craigslist. Police found what they believed to be Shannan's remains in December 2011.

The search for Shanna's body led to the discovery of a mass grave of missing people on the Long Island beach. Although Shannan's body was found on the same stretch of land where the other victims were found, police have long maintained that her death was not connected to the suspected serial killer.

A Suffolk County Police Department spokesperson said police still believe Shannan's death is not connected to the other victims – who are all believed to have been murdered by the serial killer – and noted that they have not declared Shannan a murder victim.

"With respect to Shannan Gilbert, an autopsy was completed by the Office of the Suffolk County Medical Examiner … and the cause of her death was undetermined," the spokesperson said.

Police have said that Shannan likely drowned.

But Shannan's Mother Believed Differently

Since losing Shannan, 52-year-old Mari Gilbert and her remaining daughters, Sarra and Sherre, have maintained that the woman's death was not accidental, as authorities have suggested.

Mari fought for authorities to investigate Shannan's death as a murder case and insisted that the FBI take over the search.

"We are going to continue to fight as long as we need to until justice is done for our daughter," Mari said at a press conference in February.

Mari even enlisted the help of famed forensic pathologist Michael Baden to perform an autopsy in which he determined that Shannan may have been strangled to death, NBC New York reports.

"We're demanding they activate a homicide investigation for Shannan Gilbert," family attorney John Ray told NBC in February.

The police spokesperson said detectives have requested to review Baden's report and are awaiting documentation.

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How it All Began

Melissa Barthelemy went missing from her Bronx apartment in July 2009. And police seemed sure that nothing was wrong.

"They said, 'She's 24; she's where she wants to be; she's not missing,' " her mother, Lynn, recalled to PEOPLE then.

Investigators changed their tune when Barthelemy's teen sister started receiving anonymous phone calls from a man, saying, "I killed Melissa."

Melissa's remains, and the remains of three other sex workers, were found about 10 months later when authorities began searching for Shannan. The discovery led experts to a conclusion: there was a serial killer.

"Prostitutes are probably the most common victims of serial killers," Vernon Gerberth, author of textbook Practical Homicide Investigation told PEOPLE in 2011.

Shannan's aunt, Lori Grove, told PEOPLE that it was likely her niece's status as a sex worker that caused police to pay Shannan's disappearance little attention initially.

Shannan was a prostitute, Lori said, "but does that mean she wasn't worth looking for all those months?"

The Victims

During the search for Gilbert, investigators found the remains of eight women, a child and a man dressed in women's clothing, The New York Times reported.

Officials said then that all of the victims has a possible connection to the sex trade – police said they believe the toddler found was the child of a prostitute, according to the Times.

Four of the victims, Barthelemy, Maureen Brainard-Barnes, Megan Waterman and Amber Costello, were all sex workers who had advertised on Craigslist and had been missing for months or years.

The four women were found first and, after increasing their search efforts, investigators unearthed the remains of six more bodies in the same area.

Shortly after the discoveries, families of the deceased began connecting with one another on Facebook.

"There's comfort in knowing that someone else knows that your going through," Costello's sister, Kim Overstreet, told PEOPLE in 2011. "Someone knows your pain."

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The Killer is Still at Large

The Suffolk County Police Department spokesperson said although officials do not "speak on suspects or leads," "no arrests" have been made in the case. The spokesperson added that police find themselves virtually in the same place they were at the time of the gruesome discoveries, with very little information about the killer.

"The Suffolk County Police Department is doing everything it can to solve the Gilgo Beach homicides and that is why the Department recently partnered with the FBI," police said in a February statement obtained by PEOPLE.

Among the remains found at Gilgo Beach, police linked some of the body parts to victims found several miles away since 1996, the Associated Press reports.