One key thing that Gone Girls: The Long Island Serial Killer omitted
Gone Girls: The Long Island Serial Killer, Netflix’s latest true-crime docuseries directed by Liz Garbus, revisits the long-stalled investigation into a string of murders that haunted Long Island for over a decade.
The three-part series recounts how the discovery of Shannan Gilbert’s disappearance in 2010 led to the unearthing of multiple victims’ remains along Ocean Parkway, ultimately connecting the deaths to Rex Heuermann, a Massapequa-based architect arrested in 2023.
According to a Time report dated March 31, 2025, the formation of an interagency task force in 2022 enabled investigators to digitize evidence and identify Heuermann within six weeks. The series focuses on systemic failures, media neglect, and the families who pressured law enforcement for answers.
Yet, one key element remains largely unaddressed: the 2016 murder of Shannan Gilbert’s mother, Mari Gilbert, who was killed by her daughter Sarra after years of advocacy for Shannan’s case.
As per the US Weekly report dated March 31, 2025, Mari's death occurred years before Heuermann’s arrest, a fact not acknowledged in Gone Girls: The Long Island Serial Killer.
Gone Girls: The Long Island Serial Killer mentions Shannan Gilbert but omits that her mother, Mari, was killed before Rex Heuermann’s arrest
Netflix’s Gone Girls: The Long Island Serial Killer revisits the case that remained unsolved for over a decade, the Gilgo Beach murders, primarily through the lens of Shannan Gilbert’s 2010 disappearance. Her story, which triggered the initial search that unearthed several other victims, is central to the documentary.
However, one significant detail is absent from Gone Girls: The Long Island Serial Killer: Mari Gilbert, Shannan’s mother and a key figure in the push for answers, was murdered in 2016, seven years before Rex Heuermann’s arrest. The omission is striking given Mari’s critical role in keeping the case in public view.
Mari Gilbert was fatally stabbed more than 200 times by her daughter Sarra Gilbert in July 2016. As per a CNN report dated June 6, 2024, Sarra, who had long struggled with mental illness, also bludgeoned her mother with a fire extinguisher during the attack. She later told police she had been hearing voices instructing her to kill Mari. Sarra was convicted and sentenced to 25 years to life.
This act of violence within the Gilbert family marked a grim chapter in an already tragic narrative. According to a US Weekly report dated March 31, 2025, Mari had been the “backbone of the family,” and her death came after years of public advocacy and confrontation with law enforcement over what she viewed as negligence in her daughter’s case.
In the years following Shannan’s disappearance, Mari repeatedly challenged the Suffolk County Police Department’s handling of the investigation. Shannan, who worked as an escort, disappeared on May 1, 2010, after fleeing a client’s house in Oak Beach. In a frantic 911 call, she screamed, “They’re trying to kill me,” as cited in CNN’s June 6, 2024, report.
Despite this, law enforcement initially labeled her a runaway, delaying a thorough search. It wasn’t until December 2011, more than a year later, that Shannan’s body was found in nearby marshland. The initial search, however, uncovered the remains of four other women, who became known as the “Gilgo Four.”
These women, Maureen Brainard-Barnes, Megan Waterman, Melissa Barthelemy, and Amber Costello, all worked in the s*x trade and were found wrapped in burlap along Ocean Parkway. According to the Guardian report dated March 30, 2025, police had a viable lead as early as 2010, including a physical description and vehicle make provided by Costello’s roommate.
Yet, the investigation stalled due to internal dysfunction. The same report highlights that then-police chief James Burke actively blocked FBI involvement and was later convicted of obstruction and assault in an unrelated case.
Gone Girls: The Long Island Serial Killer does acknowledge the systemic failures that slowed the investigation, citing poor interagency communication, social stigma against s*x workers, and political corruption in Suffolk County. Liz Garbus, the director, emphasizes in the series that law enforcement “deprioritized” these women’s cases and that
“their voices had been overlooked and disregarded for so long.” - The Guardian March 30, 2025.
Still, Gone Girls: The Long Island Serial Killer does not address Mari Gilbert’s violent death, an absence that undermines the depth of her contribution and the cost of her advocacy.
As per the People report dated 2024 cited in US Magazine, attorney John Ray stated,
“What Shannan’s case did is it forced the authorities to finally pursue the evidence that existed for the other girls. Shannan kept the pressure on all those years, even though she was dead.”
Yet, Ray’s client, Mari, did not live to witness the arrest of Rex Heuermann, who was charged in 2023 with seven murders, including those of the Gilgo Four, Sandra Costilla, Jessica Taylor, and Valeria Mack. He has pleaded not guilty.
By not including Mari Gilbert’s death, Gone Girls: The Long Island Serial Killer misses an essential part of the broader narrative: the personal toll on families who fought for justice in the face of indifference.
Mari’s advocacy wasn’t merely a subplot; it was foundational to the eventual formation of the 2022 interagency task force that identified Heuermann within six weeks, as TIME reported on March 31, 2025. Her absence from the series leaves a critical void in the story’s full accounting.
Gone Girls: The Long Island Serial Killer is available to stream on Netflix.
