A notorious true crime case is getting the Lifetime treatment on Saturday, Feb. 20, with the premiere of The Long Island Serial Killer: A Mother’s Hunt for Justice, which will surely cover what happened to Mari Gilbert. As she strove for answers in the death of her daughter, Shannan Gilbert, Mari was killed by another of her daughters.

As viewers also saw in the 2020 Netflix film Lost Girls, the search for Shannan’s body — which was found in December 2011, a year and a half after she disappeared — uncovered the remains of 10 people speculated to be the victims of a still-unidentified Long Island serial killer.

What happened to Mari Gilbert?

Mari was found dead in July 2016 in her daughter Sarra Gilbert’s apartment in Ellenville, N.Y. In the wake of the killing, Sarra was charged with second-degree murder and criminal possession of a weapon.

John Ray, an attorney for the family, told the New York Daily News that Sarra was “an extreme schizophrenic” who heard voices urging her to murder. “She’s a very sick, sick woman,” he added. “There’s something wrong with her. She’s not all there.”

Sarra Gilbert was sentenced to 25 years to life for Mari’s murder.

In April 2017, Sarra was convicted of second-degree murder for Mari’s death, according to the Daily Freeman, and that August, she was sentenced to 25 years to life in prison.

During the trial, the prosecution argued that Sarra killed her mother — stabbing Mari more than 200 times with a 15-inch kitchen knife and beating her with a fire extinguisher — because Mari had previously gotten Sarra arrested for killing a puppy and had gotten temporary custody of Sarra’s son.

The defense, meanwhile, contended that Sarra had suffered delusions after a lifetime of abuse and mental illness.

Nevertheless, the jury declined the option of finding Sarra “not responsible due to mental disease or defect.” One juror told the Daily Freeman, “We feel that she has mental illness but she was also aware of what she was doing. There’s no doubt everyone agreed there was definite mental illness.”

After the conviction, Ray maintained that Sarra was extremely mentally ill and said she needed to be institutionalized. “I think Sarra will kill someone in prison,” he said, the newspaper reported. “It is almost certain.”

Assistant District Attorney Emmanuel Nneji, meanwhile, also said that Sarra would kill again — if she got the chance — adding that she was a sociopath and a “selfish individual” who “has to have her way at all times.”

Kim Delaney is playing Mari Gilbert in the Lifetime movie.

In The Long Island Serial Killer: A Mother’s Hunt for Justice, actress Kim Delaney — best known for her roles on the TV shows NYPD Blue and Army Wives — is playing Mari and portraying her search for answers.

“After Shannan (Katharine Isabelle, Hannibal) fails to come home, her mother Mari knows something is terribly wrong,” Lifetime says in a synopsis for the TV movie. “Pleading to police to take her concerns seriously, she keeps pushing the police for answers. Mari’s insistence that her daughter not be overlooked eventually leads to a horror hidden on Long Island for more than a decade.”

The Long Island Serial Killer: A Mother’s Hunt for Justice premieres Saturday, Feb. 20, at 8 p.m. EST on Lifetime.