EXCLUSIVE: HBO Documentary Films has acquired the rights to journalist Michelle McNamara’s bestselling true-crime book I’ll Be Gone in the Dark: One Woman’s Obsessive Search for the Golden State Killer, to develop as a docuseries.

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I’ll Be Gone in the Dark is a meticulous exploration of the case of an elusive, violent predator who terrorized California in the late 1970s and early ’80s. McNamara, the late wife of Patton Oswalt, was in the midst of writing the book when she unexpectedly died in her sleep in 2016. The book was completed by McNamara’s lead researcher Paul Haynes and a close colleague, Billy Jensen, and framed by an introduction by Gillian Flynn and afterword by Oswalt, who also executive produces the docuseries.

McNamara’s I’ll Be Gone in the Dark is described as a chilling investigation of the mysterious serial killer and the wreckage he left behind, as well as a compelling self-portrait of the author that reveals her obsession with solving crimes and her unflagging search for the truth and justice for the victims and their families.

“HBO taking on this story will advance the passionate pursuit that Michelle shared with dozens of men and women in law enforcement – to solve the mystery of one of California’s most notorious serial killers,” said Oswalt.

Creator of the popular website TrueCrimeDiary.com, McNamara was determined to find the violent psychopath she dubbed “The Golden State Killer” — who committed 50 home-invasion sexual assaults in Northern California before moving south, where he perpetrated 10 murders. Then he disappeared, eluding multiple police forces and some of the best detectives in the area.

Obsessed with the case three decades later, McNamara pored over police reports, interviewed victims and embedded herself in the online communities that were as obsessed with the case as she was. I’ll Be Gone in the Dark also explores McNamara’s own past, including her years growing up in a large family in Oak Park, IL, and the reverberations of the unsolved murders that haunted her youth.

Published this year by HarperCollins, I’ll Be Gone in the Dark debuted at No. 1 on The New York Times combined print and ebook bestseller list.

Oswalt and the Estate of Michelle McNamara are repped by UTA and attorney Lev Ginsburg.