In the years between 1976 and 1986, the East Bay Rapist sexually assaulted around 50 women and murdered at least 10 people in California. His method was to invade the ranch-style homes of couples, force the woman to tie up her spouse or boyfriend, and then bind and rape the woman.

He never stole money or valuables. Instead he would grab odd objects, like cuff links, and he would often forage in the refrigerator, helping himself to a post-assault snack.

The East Bay Rapist, the late author Michelle McNamara writes in the chilling true-crime book, “I’ll Be Gone in the Dark,” “was white, in his late teens or twenties, about five foot nine, with a medium, athletic build. Always in some sort of mask. Forced, angry whisper. Clenched jaw. When he got upset, his voice rose to a higher pitch.”

Despite the later evolution of DNA evidence and sophisticated geographic profiling the East Bay Rapist was never caught. To date, some 8,000 suspects have been investigated.

McNamara’s obsession with the East Bay Rapist is what drives this book. McNamara died when the book was about half-finished (it was completed by her lead researcher, Paul Haynes, and investigative journalist Billy Jensen). But during her work on the book, it took over her life — she left parties abruptly, unwilling to be away from her research even for an evening. One night she woke from a sound sleep when her husband tiptoed into their bedroom, and she leapt out of bed and swung a lamp at his head.

Her dogged reporting makes “I’ll Be Gone in the Dark” both hard to read and hard to put down. The accounts from survivors are nightmarish and the crime scenes of the homicide victims are disturbing.

And, she suggests, the rapist is still out there, still alive. Twenty-four years after a sexual assault, the rapist phoned a victim and whispered, “Remember when we played?”

Addressing him directly in the Chapter “Letter to an Old Man,” McNamara writes, “I imagine you dialing her number, alone in a small, dark room, sitting on the edge of your twin bed, the only weapon left in your arsenal firing up a memory, the ability to trigger terror with your voice.”

Stephen J. Lyons is the author of four books, most recently “Going Driftless: Life Lessons From the Heartland for Unraveling Times.”

I'll Be Gone in the Dark
By: Michelle McNamara.
Publisher: Harper, 328 pages, $27.99.