Police believe Janelle Cruz, right, was murdered by Golden State Killer suspect James Joseph DeAngelo in 1986. (Photo courtesy of Michelle Cruz)

The noise startled Janelle Cruz and her friend enough to warrant a look out the window, but they didn’t see anything suspicious when they peered into the darkness. It was probably a cat, they thought.

A few minutes later, they heard a noise from the garage, family members told The Washington Post. It sounded like a door closing or perhaps an outside gate. But, again, nothing stood out when they took a look.

Still, Cruz’s friend was a little spooked. And it was 10:45 at night, getting late, time for him to be on his way.

Most of the Cruz family was on vacation that night in May 1986, but Janelle Cruz had a new job at a nearby pizza joint and had stayed at home in Irvine, Calif., near Los Angeles, to clock some hours.

The 18-year-old’s family and her visitor had left — but Cruz was not home alone.

The next day around 5 p.m., a real estate agent who had planned to show the home to potential buyers found the teenager, raped and bludgeoned to death in her bed.

Authorities believe Cruz was the final victim of the “Golden State Killer,” who was accused of raping 45 people and killing 12 in California in the 1970s and 1980s. Joseph James DeAngelo, a 72-year-0ld former police officer, was charged with several murders on Wednesday, including Cruz’s.

For three decades, investigators believe, he was the only person alive who knew what happened in the 18 hours between Cruz’s goodbye with her friend and the discovery of her battered body.

The evidence investigators encountered pointed to a brutal rape and murder.

Police found blood on the kitchen floor, blood on the cabinets, blood on the wood floor by the front door, blood on the home’s wood shutters, and blood at the head of Cruz’s bed.

They recovered blue lint on and around Cruz’s body, from what authorities determined were pieces of fabric that had been ripped. In previous attacks, the Golden State Killer tore up towels and used them as blindfolds, gags and restraints.

Cruz had been struck in the back of the head, possibly with a pipe wrench that was missing from the home’s back yard. Her face had also been battered, and she had taken a serious blow to her forehead.

The booking photo of Joseph James DeAngelo, 72. (Sacramento Sheriff’s Office)

No one knows why the Golden State Killer stopped his string of violent crimes after Cruz’s death, as The Post reported. In all, he had slain a dozen people and raped 45, sometimes in front of bound loved ones who were forced to watch.

DeAngelo went on to become a father, then a grandfather, in Citrus Heights, Calif., known for his meticulous lawn and bad temper.

He was training to be a police officer around the time of the first attacks, a profession that may have helped him evade suspicion.

Cruz, meanwhile, seemed to be escaping the tumult of her troubled teenage years. She had twice been put into a psychiatric hospital and still had telltale cuts on her wrists from self harm, Los Angeles Magazine reported in 2013.

Still, a 10-month stint at Job Corps in Utah had been successful. She had gotten a part-time job at Bullwinkle’s Pizza, where she had met the friend who came to her house on her last night alive.

It’s unclear how much of that the Golden State Killer knew when he walked into her bedroom. He was a serial killer who meticulously studied would-be victims — and secretly watched them.

The sounds Cruz heard and dismissed were probably from her killer, stumbling around in the dark, Orange County District Attorney Investigator Erika Hutchcraft told CBS News.

“We know he’s a peeper, we know he’s a prowler and he likes to watch people,” Hutchcraft said. “So we know he was probably watching her with her friend and then he was able to watch the male friend leave, so he knew that she was alone.”

The location of Cruz’s one-story, brick and stucco house may have also been attractive to the killer. It’s at the end of a cul-de-sac, near a hedge-flanked pedestrian access point that led to a nearby park. That would make it easier for someone to move around without being seen.

No one spotted Cruz’s killer that night — or for the next three decades.

It wasn’t until 2001 that investigators using DNA collected from a variety of crime scenes realized that her killer was connected to other crimes, all victims of the Golden State Killer, The Post reported.

By then, it had been more than a decade since anybody named Cruz had set foot in the house at 13 Encina.

“Our family unit had been shattered,” her sister Michelle Cruz told Oxygen.

They buried Janelle Lisa Cruz in a white dress and stayed away from the place that was a constant reminder of her brutal death. “We never went back to that house. We sold it.”

On Thursday, nearly 32 years later, Michelle Cruz’s memory turned back to her older sister.

“Janelle Lisa Cruz. Sister, best friend, killed by the Golden State Killer,” she tweeted. “She can now RIP.”

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