Mari Gilbert Refused To Let Police Ignore Her Daughter’s Disappearance — And It Led Them To A Serial Killer

Published April 25, 2024
Updated May 20, 2024

Mari Gilbert became an advocate for murder victims after her daughter Shannan's disappearance led to the discovery of the Gilgo Beach Murders — then Mari was killed herself by her other daughter Sarra.

When Mari Gilbert’s daughter, Shannan Gilbert, vanished in May 2010, the grieving mother spent more than a year pressuring police to take her disappearance seriously. She had no idea that her perseverance would lead to the arrest of a suspected serial killer.

Mari Gilbert

Tribune Content Agency LLC / Alamy Stock PhotoMari Gilbert holding a poster with photos of her daughter Shannan Gilbert and the four Gilgo Beach Murder victims in May 2011.

While investigating Shannan’s case, authorities came across the bodies of 10 other people — many of whom were sex workers — buried on the South Shore of Long Island. And in December 2011, Shannan’s body was discovered in a marsh nearby.

Gilbert soon became an outspoken murder victims’ advocate, especially for sex workers. She claimed their cases weren’t taken seriously because of their occupation, and she wanted to change that.

Tragically, Gilbert was stabbed to death by her other daughter, Sarra Gilbert, in July 2016. In a shocking turn of events, the murder victims’ advocate became a murder victim herself.

The Disappearance Of Shannan Gilbert

In the early morning hours of May 1, 2010, 23-year-old Shannan Gilbert called 911 in a panic. She was working as an escort at the time, and she had been at a client’s house in Oak Beach on Long Island for several hours. While on the phone with dispatchers, Shannan was seen running down the street knocking on doors and shouting for help. However, the police didn’t arrive for nearly an hour.

By then, Shannan was nowhere to be found. Despite the suspicious circumstances, detectives dragged their feet during the investigation. Shannan’s mother, Mari Gilbert, claimed that authorities weren’t treating her daughter’s disappearance with urgency because she was a sex worker.

Shannan Gilbert

Praying for Shannan Maria Gilbert/FacebookShannan Gilbert was 23 years old when she vanished from Oak Beach on Long Island in May 2010.

“I think they look at them like they’re throwaway,” Gilbert told The New York Times in 2011. “They don’t care.”

Gilbert spent the next 18 months putting more and more pressure on police to find out what had happened to her daughter. In the end, this persistence paid off with the discovery of Shannan’s body in December 2011 — but it uncovered an even bigger mystery, too.

How Mari Gilbert Helped Find The Long Island Serial Killer

In December 2010, police were searching an area near where Shannan Gilbert had vanished with a cadaver dog when the K-9 alerted on something. It was a body — but it wasn’t Shannan’s.

Detectives soon discovered the corpses of four women all buried within half a mile of each other near Gilgo Beach. All of them were sex workers who had used Craigslist to find clients. They’d vanished between 2007 and 2010, and all four are believed to have been victims of the Long Island Serial Killer.

Police continued to search the area, and by April 2011, they’d discovered six more bodies along the South Shore of Long Island. At least three of them were also sex workers. The other three — who remain unidentified — were a mother, her toddler, and an Asian male.

Amy Ryan As Mari Gilbert

Entertainment Pictures / Alamy Stock PhotoAmy Ryan as Mari Gilbert in the 2020 Netflix thriller Lost Girls.

Then, in December 2011, authorities found Shannan Gilbert’s body in a marsh near Oak Beach, about nine miles from the other bodies. However, they claimed that she hadn’t been killed but instead had accidentally drowned. Mari Gilbert immediately challenged this theory and had an independent autopsy performed — which showed that Shannan may have been strangled to death.

“It’s time… for the police department to wise up,” said the Gilbert family’s attorney, John Ray, as reported by CNN in 2016. “It’s time now for the police department to do the job that they have failed to do up until now and to investigate the death of Shannan Gilbert as a murder.”

Mari Gilbert was determined to spend the rest of her life seeking justice for her daughter — but her efforts were tragically cut short in 2016.

The Brutal Murder Of Mari Gilbert

While Mari Gilbert was busy working to figure out what exactly had happened to Shannan, she was juggling problems with one of her other daughters, 27-year-old Sarra Gilbert, as well.

Sarra suffered from schizophrenia, and when she drowned her pet dog in front of her eight-year-old son in February 2016, Mari took custody of the boy, according a 2016 article in the Middletown Times Herald-Record.

Sarra Gilbert

Ellenville Police DepartmentSarra Gilbert was sentenced to 25 years to life in prison for Mari Gilbert’s death.

Then, on July 23, 2016, Sarra reportedly started hearing voices and called her mother for help. Mari raced to Sarra’s apartment in Ellenville, New York. “Mari loved her daughter,” Ray told CNN. “She went to her death… knowing when she was going to that house that she was in danger.”

When Mari arrived, Sarra stabbed her 227 times with a 15-inch kitchen knife. She then bashed her in the head with a fire extinguisher and sprayed foam from the device into her mouth. Sarra also reportedly tried to cut off Mari’s head because she thought she was “a bad god” and “a devil.”

Sarra pleaded not guilty by reason of insanity, but she was ultimately sentenced to 25 years to life in prison for Mari Gilbert’s death.

The Legacy Of Mari Gilbert

Although Mari Gilbert’s life was cut short at age 52, her legacy as a murder victims’ advocate lives on. She never gave up on finding out what had really happened to her daughter Shannan.

“She was not perfect,” Mari said about Shannan in 2011, “but she was loved and she was cared for. She does not deserve to be forgotten.”

Mari Gilbert also found comfort in the fact that the pressure she put on police helped uncover the bodies of 10 other victims, hopefully bringing closure to their families.

“Mari understood that one way of finding at least a shred of meaning in the loss of her daughter was that her disappearance led to the discovery of those four women several months later, and that without Shannan there would be no case, there would be no search for the killer,” said Robert Kolker, the author of a book that delved into the Gilgo Beach Murders, to CBS News in 2023.

In July 2023, a Long Island man named Rex Heuermann was arrested and charged with the murders of three of the women found on Gilgo Beach in December 2010. And in January 2024, he was charged in connection with the fourth woman’s death as well. He is currently awaiting trial.

Rex Heuermann

ZUMA Press, Inc. / Alamy Stock PhotoRex Heuermann was arrested in 2023 for the Gilgo Beach Murders, but he hasn’t been connected to Shannan Gilbert’s death.

Without the persistence of Mari Gilbert, however, those four women — and the six other victims who were uncovered alongside them — may still be buried in the sand, and their families may still be wondering where they are.

According to Kolker, Mari “reminded people that there were real human beings at stake here, that this wasn’t just a Hannibal Lecter movie.”

“She was not a perfect person,” continued Kolker, “and she was a confrontational person. But in her final years, she became the caregiver for another sick daughter of hers… [S]he had grown as a person and really found a way to keep living despite such terrible loss.”

Today, Mari Gilbert’s daughter Sherre runs the Facebook page Praying for Shannan Maria Gilbert, which Mari started years ago to gather information about her daughter’s case and form a support system for others who have lost loved ones.

Mari’s story also lives on in the 2020 thriller Lost Girls, a fictionalized account of the bereaved mother’s dedicated hunt for her daughter and the discovery of the Gilgo Beach Murder victims.

After reading about the tragic life and death of Mari Gilbert, go inside the story of Richard Cottingham, the Times Square Torso Killer who brutally murdered dozens of sex workers between 1979 and 1980. Then, learn about Bobby Joe Long, Florida’s “Classified Ad Rapist.”

Rivy Lyon
True crime expert Rivy Lyon holds a Bachelor's degree in criminology, psychology, and sociology. A former private investigator, she has also worked with CrimeStoppers, the Innocence Project, and disaster response agencies across the U.S. She transitioned into investigative journalism in 2020, focusing primarily on unsolved homicides and missing persons.
Cara Johnson
A writer and editor based in Charleston, South Carolina and an assistant editor at All That's Interesting, Cara Johnson holds a B.A. in English and Creative Writing from Washington & Lee University and an M.A. in English from College of Charleston and has written for various publications in her six-year career.
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Cite This Article
Lyon, Rivy. "Mari Gilbert Refused To Let Police Ignore Her Daughter’s Disappearance — And It Led Them To A Serial Killer.", April 25, 2024, Accessed May 23, 2024.