“True crime has become such an explosive industry and one of the things we wanted people to understand was how seminal her work was,” Garbus explained during a pre-recorded panel for the ATX TV…from the Couch festival on Friday. “She really was a pioneer.”

In 2016, McNamara was in the midst of writing the true crime book “I’ll Be Gone in the Dark” — about the hunt for the “Golden State Killer,” whom authorities had been working to identify since the 1970s — when she suddenly passed away in her sleep. In 2017, her husband, the actor Patton Oswalt, revealed that she died from a combination of prescription medications and an undiagnosed heart condition.

Following her death, Oswalt, crime writer Paul Haynes and investigative journalist Billy Jensen finished McNamara’s book and published it in February 2018.

Just months later, accused “Golden State Killer” Joseph James DeAngelo was arrested and charged with 13 counts of murder and multiple kidnapping and weapons charges.

Garbus said producers of the film wanted to make sure to keep McNamara’s literary voice and highlight her writing in the upcoming series.

“She had [this incredible way] with words, which always showed such empathy and connection with the survivors,” she said.

Filmmakers also felt a responsibility to keep in mind the family she left behind, including Oswalt and their 11-year-old daughter, Alice, Garbus said.

“I’ll Be Gone in the Dark,” a six-part docuseries, premieres on HBO on June 28.