By DON THOMPSON, Associated Press

SACRAMENTO, Calif. (AP) — Forty years ago, kids rode their bikes unsupervised through suburban bedroom communities bracketed by Air Force bases east of Sacramento, California. Families rarely locked their doors at night.

"It was a time of innocence. And then in June of 1976, that all changed," Sacramento County District Attorney Anne Marie Schubert recalled about growing up in the area. "A community was taken hostage."

The tranquility was shattered by an elusive, violent attacker who authorities say committed at least 45 rapes in the region along with at least 12 homicides and dozens of burglaries across California over the next decade.

He was initially dubbed the East Area Rapist after beginning his crimes in Northern California. He later became known as the Original Night Stalker for a series of slayings in Southern California before investigators realized he was one and the same person.

Now called the Golden State Killer, he has been linked through DNA and other evidence to scores of crimes.

"This serial offender was probably one of the most prolific, certainly in California and possibly within the United States," said Sacramento County sheriff's homicide Sgt. Paul Belli.

A generation of investigators has grown old and retired since the hunt began. Four decades of frustration later, the FBI on Wednesday announced a $50,000 reward and a national media campaign to track down the killer who would now be 60 to 75 years old.

Authorities decided to publicize the case in advance of June 18 — the 40th anniversary of his first known assault in Sacramento County. Belli said investigators are looking for clues concerning other crimes in California and elsewhere that he may have committed.

A telephone recording released by the FBI through its website, https://www.fbi.gov/sacramento , provides a chilling verbal glimpse of the killer: "I'm gonna kill you. Gonna kill you. Gonna kill you," he breathes to one of his rape victims in a message she recorded sometime after the attack.

The masked rapist, armed with a gun, would break into homes while single women or couples were sleeping. He would tie up the man and pile dishes on his back, then rape the woman while threatening to kill them both if the dishes tumbled.

He often took souvenirs, notably coins and jewelry, from his victims, who ranged in age from 13 to 41.

One victim recalled waking up with a hand over her mouth before she was hit, blindfolded, gagged with a sock and bound at her legs and hands. The rapist "put me back in bed and said if you move, I'm going to kill you," she said in a recorded interview released by the FBI.

"You're laying there thinking you're going to die," she said. Her name was not released.

Investigators believe the rapes and dozens of burglaries that were often used to scout neighborhoods escalated in 1978, when the killer fatally shot U.S. Air Force Sgt. Brian Maggiore and his wife Katie as they walked their dog.

The rapes were committed near military bases, so investigators said some people who might be able to provide clues likely moved elsewhere long ago. Authorities believe the killer might have had an interest in the military or law enforcement, in part because he was proficient with firearms.

They suspect he moved on from suburban Sacramento to commit several rapes in the San Francisco Bay Area before heading to Southern California.

It wasn't until 2001 that new DNA testing linked him to at least six homicides there between 1979 and 1986. In each case, the killer broke into a house at night, then raped and killed a female victim.

The Southern California killer had been called the Original Night Stalker to distinguish him from Night Stalker Richard Ramirez, who died of cancer in 2013 before he could be executed for committing 13 mutilation killings in 1984 and 1985.

The killer now being sought was also briefly known as the Diamond Knot Killer for an elaborate knot he used to tie up a Ventura couple before they were beaten to death with a fireplace log in 1980.

The killer was described at the time as white, about 5 feet 9 inches with blonde or light brown hair.

"The victims and their families deserve justice," said Monica Miller, special agent in charge of the FBI region. "The victims and families ... still bear emotional scars from this horrific experience."