Shannan was last seen at a clients home in Oak Beach, Long Island, on May 1, 2010, where she made a 22-minute call to 911 before running away on foot and disappearing. It would take the Suffolk County police department more than a year to uncover the 24-year-olds body just half a mile from where she was last seen, per NBC News . Things took an eerie turn when, during their search, they discovered the bodies of 10 others (eight women, one man in women's clothing, and a toddler) along the shore near Oak Beach and Gilgo Beach just nine miles away. Investigators came to suspect those 10 people were targeted by a serial killerone who would eventually be known as the Long Island Serial Killer and Gilgo Beach Killer.

Considering the close locations, you might think authorities would have counted Shannan among the suspected serial killers victims, but they didnt. Instead, investigators maintain there was no foul play in Shannans case. They say she got caught up in the muddy brush and bramble of the marsh and drowned, per NBC.

This is a conclusion Shannans mother, Mari Gilbert (played by Oscar-nominated Amy Ryan from The Office and The Wire), wasnt satisfied with. Until her own murder in 2016, Mari and the Gilbert family's estate lawyer, John Ray, believed Shannan was killed. They called for the police to release the recordings of Shannans 911 call in the hopes someone would come forward. To this day, authorities still havent made these tapes public. Its a suspicious refusal that makes it seem like theres way more to this story.

Here's everything you need to know about the real-life Shannan Gilbert and how the investigation into her death opened so many others:

How and where was Shannan Gilberts body found?

Shannans body was discovered by police on December 13, 2011 in a marsh at Oak Beach. Her purse and cell phone were found a few days earlier, just a quarter mile from where she was found dead, per Oxygen . Police wont budge on the drowning theory, but after the police-ordered autopsy, the medical examiner ruled her cause of death inconclusive.

Shannans family commissioned their own autopsy which concluded Shannons injuries were "consistent with homicidal strangulation," according to NBC .

Why did Shannans mom, Mari Gilbert, doubt the police?

She believed Shannans death was linked to the 10 other murders based on the independent examination conducted by former New York City medical examiner Michael Baden, MD. Dr. Baden said there was no evidence indicating Shannan drowned, succumbed to the elements, or overdosedthe theories Suffolk Country authorities were pushing, per NBC .

One piece of evidence that could settle these conflicting theories could be the recordings of Shannan's 911 call, during which she reportedly told the operator, "They are trying to kill me," according to Former Suffolk County Chief of Detectives Dominick Varrone. In an interview with 48 Hours , he recalled, "She's saying, 'There's someone after me; there's someone after me.' It's a girl who clearly believes...she's in harm's way."

Shannans last client, Joseph Brewer, and neighbors in Oak Beach made additional calls to the police that evening as well, according to Oxygen. But, since authorities are stalling their release, the Gilbert family may never know.

In 2012, Mari first attempted to get the tapes released by having Ray request them under the Freedom of Information Act. He was denied. The police dug in their heels and insisted Shannan drowned. Well, if Shannans death wasnt a homicide, whats the harm in releasing the audio? Thats precisely what the Gilberts would like to know.

So, will the recordings of Shannans 911 call ever be released?

Maybe. After Maris murder, Ray tried twice to get the tapes again in 2018 with a court order, per Oxygen . The police were given 20 days to make the calls and their transcripts public. But instead of complying, the Suffolk County Police Department stalled the process with an appeal.

The police commissioner claimed releasing the tapes would tamper with an ongoing investigation. A statement Ray, again, found suspicious considering law enforcement have long held onto their theory that Shannan wasnt murdered. If the investigation is ongoing, the police either cant be too sure about their original conclusion or theyve tampered with the evidence and dont want to be found out, Ray says. The courts now have until late March 2020 to decide whether theyll side with the police or the Gilbert family.

"If theres nothing of significance criminally, on the tapes, we have a family that wants to hear [Shannans] voice and we have a civil reason to have the tape. Theres no reason to not give them up unless they are important criminally," Ray told Oxygen. "If they are, then theres either something on the tape they dont want us to hear, maybe evidence or they erased the tape or doctored it. Otherwise, there cant be a reason to hold them back."

What about the other 10 bodies that were found?

Investigators and K-9 units discovered the remains of 10 other people and dismembered body parts during their search for Shannaneight female bodies, one male dressed in womens clothing, and a toddler. Detectives confirmed four of the people found were escorts, like Shannan, who used Craigslist and Backpage to post about their services. The toddler was the daughter of one of the dead women.

How was Shannan's mother, Mari Gilbert, killed?

Mari was stabbed to death by her other daughter and Shannans younger sister, Sarra, in July of 2016. Sarra, who was diagnosed with schizophrenia, was sentenced to 25 years in prison in 2017 after pleading not guilty by reason of insanity.

For the six years following Shannans death, Mari insisted the police take her daughters death more seriously and investigate it as a homicide. Maris murder meant the biggest advocate for uncovering the truth about Shannans death was gone.

"I'm going to keep fighting for my daughter and for my family until the truth comes out," Mari said when Shannans body was recovered. "No matter how long it takes."

Do the police currently have any leads?

There have been no arrests in connection with Shannans death, and the suspected Long Island Serial Killer is still at large.

In fact, according Judge Sanford Berland (who called for the release of the 9-1-1 tapes) said, "No criminal prosecution is pending nor, so far as can be discerned from the police department's bare assertions, is it anticipated that a criminal prosecution will be brought within any time frame that the police department is currently willing, or able, to articulate," according to NBC.

However, the day the trailer for Lost Girls was released, investigators made a "previously undisclosed piece of evidence" publicphotos of a belt taken at the crime scene with either the letters WH or HM embossed on it. Authorities believe it was handled by the killer, according to NBC New York .

The Gilbert familys theory is Shannans death, which they believe to be a homicide, involved Peter Hackett, MD, a doctor from Oak Beach who called Mari and said, "I run a home for wayward girls" two days after Shannan disappeared, according to Vice .

Dr. Hackett has long denied this claim, but phone records say otherwise. Actually, according to the records, Dr. Hackett called Mari twice. Eventually, he admitted to the calls, but maintains he never met Shannan.

The Gilberts dont buy it. They filed a civil lawsuit against the physician in November 2012 and claim he took Shannan in the morning she disappeared and drugged her, which played a part in her death.