This piece is excerpted from “I’ll Be Gone in the Dark: One Woman’s Obsessive Search for the Golden State Killer,” which was published on February 27th by HarperCollins. The Golden State Killer is the name McNamara gave to an unidentified man who raped more than fifty women and likely killed ten or more people in California in the nineteen-seventies and eighties. Several years ago, McNamara began investigating the case and blogging about it on her Web site. She died in April, 2016, at the age of forty-six.

You were your approach: The thump against the fence. A temperature dip from a jimmied-open patio door. The odor of aftershave permeating a bedroom at 3 A.M. A blade at the base of the neck. “Don’t move, or I’ll kill you.” Their hardwired threat-detection systems flickered meekly through the sledgehammer of sleep. No one had time to sit up. Awakening meant understanding that they were under siege. Phone lines had been cut. Bullets emptied from guns. Ligatures prepared and laid out. You forced action from the periphery, a blur of mask and strange, gulping breaths. Your familiarity freaked them. Your hands flew to hard-to-find light switches. You knew names. Number of kids. Hangouts. Your preplanning gave you a crucial advantage, because, when your victims awoke to the blinding flashlight and clenched-teeth threats, you were always a stranger to them, but they never were to you.

Hearts drummed. Mouths dried. Your physicality remained unfathomable. You were a hard-soled shoe felt fleetingly. A penis slathered in baby lotion thrust into a pair of bound hands. “Do it good.” No one saw your face. No one felt your full body weight. Blindfolded, the victims relied on smell and hearing. Floral talcum powder. Hint of cinnamon. Chimes on a curtain rod. Zipper opening on a duffel bag. Coins falling to the floor. A whimper, a sob. “Oh, Mom.” A glimpse of royal-blue brushed-leather tennis shoes.

The barking of dogs fading away in a westerly direction.

You were what you left behind: a four-inch vertical cut in the window screen at the ranch house on Montclair, in San Ramon. A green-handled hatchet on the hedges. A piece of cord hanging in a birch tree. Foam on an empty Schlitz Malt Liquor bottle in the back yard. Smears of unidentifiable blue paint. Frame 4 of Contra Costa County Sheriff Department’s Photo Roll 3, of the spot where they believe you came over the fence. A girl’s purpled right hand, which was numb for hours. The outline of a crowbar in dust.

Eight crushed skulls.

You were a voyeur. A patient recorder of habits and routines. The first night a husband working dispatch switched to the graveyard shift, you pounced. There were four-to-seven-day-old herringbone shoe impressions beneath the bathroom window at the scene on the 3800 block of Thornwood, Sacramento. Officers noted that, standing there, you could stare into the victim’s bedroom. “Fuck me like your old man,” you hissed, like you knew how that was done. You put high heels on one girl, something she did in bed with her boyfriend. You stole bikini Polaroids as keepsakes. You stalked around with your needling flashlight and clipped, repetitive phrases, both director and star of the movie unspooling in your head.

Almost every victim describes the same scene: a time they could sense you return after a period of distracted ransacking in another part of the house. No words. No movement. But they knew you were standing there, could imagine the lifeless gaze coming from the two holes in your ski mask. One victim felt you staring at the scar on her back. After a long while of hearing nothing she thought, He’s gone. She exhaled, just as the knife tip came down and began tracing the end of the scar.

Fantasy adrenalized you. Your imagination compensated for failed reality. Your inadequacies reeked. One victim experimented with reverse psychology and whispered, “You’re good.” You abruptly got off her, amazed. Your tough-guy bravado smelled like a bluff. There was a shakiness to your clenched-teeth whisper, an occasional stutter detected. Another victim described to police how you’d briefly grabbed her left breast. “Like it was a doorknob.”

“Oh, isn’t this good?” you asked one girl as you raped her, and held a knife to her throat until she agreed.

Your fantasies ran deep, but they never tripped you up. Every investigation into an at-large violent offender is a footrace; you always maintained the lead. You were savvy. You knew to park just outside the standard police perimeter, between two houses or on a vacant lot, to avoid suspicion. You punched small holes in glass panes, used a tool to nudge wooden latches, and opened windows while your victims remained asleep. You turned off the A.C. so you could hear if someone was coming. You left side gates open and rearranged patio furniture so you had a straight shot out. Pedalling a ten-speed, you escaped an F.B.I. agent in a car. You scuttled across roofs. In Danville on July 6, 1979, a tracker’s dog reacted so strongly to an ivy shrub on Sycamore Hill Court that the tracker believed the scent pool was just moments old.

A neighbor witnessed you escape the scene of one attack. You exited the house the way you entered: without pants.

Helicopters. Roadblocks. Citizen patrols taking down plate numbers. Hypnotists. Psychics. Hundreds of white males chewing on gauze. Nothing.

You were a scent and shoe impressions. Bloodhounds and detectives tracked both. They led away. They led nowhere.

They led into the dark.

For a long time, you have the advantage. Your gait is propulsive. In your wake are the police investigations. The worst episode in a person’s life is recorded in sloppy cursive by an often rushed and sleepy officer. Misspellings abound. Pubic-hair texture is described by a doodle in the margin. Investigators follow leads using slowly dialled rotary phones. When no one is home, the phone just continues to ring. If they want to look up an old record, they dig through stacks of paper by hand. The clattering Teletype machine punches messy holes in paper tape. Viable suspects are eliminated based on their mothers’ alibis. Eventually, the case report is put in a file, a box, and then a room. The door is shut. Yellowing of paper and fading of memory commence.

The race is yours to win. You’re home free; you can feel it. The victims recede from view. Their rhythm is off, their confidence drained. They’re laden with phobias and made tentative by memory. Divorce and drugs beset them. Statutes of limitations expire. Evidence kits are tossed for lack of room. What happened to them is buried, bright and unmoving, a coin at the bottom of a pool. They do their best to carry on.

So do you.

But the game has lost its edge. The script is repetitive and requires higher stakes. You began at windowsills, then crossed inside. The fear response stirred you. But, three years in, grimaces and pleading will no longer suffice. You yield to your darker impulses. Your murder victims are stunners all. Some have complicated love lives. To you, I’m certain, they are “whores.”

It was a different set of rules. You knew you had at least fifteen minutes to flee a neighborhood when your victims were left bound and alive in their homes. But when you walk out of Lyman and Charlene Smith’s, in Ventura, on March 13, 1980, you feel no need to rush. Their bodies won’t be found for three days.

Fireplace log. Crowbar. Wrench. You kill your victims with objects picked up at their homes—unusual, maybe, but then it’s always been your habit to be fleet of foot and encumbered by very little but rage.