Netflix’s new true crime drama, Lost Girls, tells the story of the hunt for the Long Island serial killer, who’s believed to have murdered at least 10 people and buried their bodies near a beach on Long Island, New York. The film doesn’t focus on the still-unknown killer or the official investigation into the killings, but on the grieving mothers and sisters turned victim advocates who pushed the police and media to take the murders of their loved ones seriously. At the heart of these efforts was Mari Gilbert (played in the movie by The Office’s Amy Ryan), who worked to bring attention to the the murder of her 24-year-old daughter, Shannan. Here’s what you should know.