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Investigators tracked down relatives of the "Happy Face" serial killer's last unknown victim, as they inch closer to identifying a woman named "Claudia."

Keith Hunter Jesperson, who admitted to murdering at least eight women in different states, met a hitchhiker that he called "Claudia" in Victorville, California, who wanted a ride to Los Angeles. 

He drove her toward Southern California, where a heated argument at a rest stop escalated to murder, and Jesperson dumped her body on the side of the road in the city of Blythe in eastern Riverside County, where she was found in August 1992.

It is unclear if "Claudia" is the victim's real name, but the Riverside County District Attorney's office tracked down her living relatives through DNA, but no one has been a biological match to her mom, and her dad died years ago.

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Keith Jesperson mugshot from 1995

Keith Jesperson, now 68, told police in 1996, a year after his arrest in connection with seven other homicides, that he killed an unknown woman by the name of "Susan" or "Suzette" in August 1994 and dumped her body near an exit off Interstate 10 in Florida. (Okaloosa County Sheriff)

The victim's half-sister, Summer Gonzales, was blindsided about a year ago, when law enforcement told her she had a half-sister. 

DNA testing determined Gonzales' father was also the victim's father, according to a report by CBS 8.

"I want to get justice and to find the truth for my sister," Gonzales told the local news outlet.

WATCH: "HAPPY FACE" KILLER ADMITS TO MURDERING AN EIGHTH VICTIM

She wasn't surprised that her father, whom she called a "ladies' man," fathered a child with another woman, but she expressed frustration with Riverside officials because they still won't release her sister's remains to the family, so they could have a funeral.

"It would be nice to know her real name. It would be wonderful if I could find her mother's name so that I could include those items on her tombstone," Gonzales told CBS 8. 

"But I know that she is my blood. And I want to lay her to rest with her family. I'm sure that she would have wanted that, too."

Latest rendering of "Claudia," who was the last unknown victim tied to "Happy Face" serial killer

This is the latest sketch of "Claudia," who is the "Happy Face" serial killer's last unknown victim found in Riverside County, California. It is unknown if "Claudia" was her real name. (Riverside County District Attorney's Office)

The prosecutor's office released an updated sketch and description of "Claudia," with the hope that new tips will lead to her identification. 

"This woman is the last of all his victims to remain unidentified," Riverside County District Attorney Mike Hestrin said in a video posted on YouTube. "Our goal is to identify this victim and provide closure to her family, wherever they may be.

"We are hopeful someone hearing any of these details may remember anything that could help us reunite this woman with the family who may have been looking for her for over three decades."

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"Claudia" was likely between 20 and 30 years old, about 5-feet, 6-inches to 5-feet, 7-inches tall and likely weighed around 140–150 pounds. She was described as medium build, with shaggy blonde hair that she may have dyed brown and often hitchhiked and smoked cigarettes.

She was found wearing a shirt printed with a picture of a motorcycle, and she sported a tattoo of two small dots on the left side of her right thumb. 

Picture of the tattoo on Claudia's thumb that might help ID her

The victim had a tattoo of two dots on her thumb, according to investigators. (Riverside County District Attorney's Office)

The "frequent hitchhiker," as prosecutors called her, most likely lived in Southern California, possibly Los Angeles, San Bernardino, areas in Riverside County, and may have had ties to Las Vegas and the southern Nevada area, according to the DA's office. 

Jesperson, now in his late 60s, was originally arrested in 1995 in connection with a woman's murder in Washington state. 

ONE OF ‘HAPPY FACE’ KILLER'S EIGHT VICTIMS ID'D AFTER NEARLY THREE DECADES

His case became infamous after eventually confessing to killing eight women between 1990 and 1995 in California, Washington, Oregon, Florida, Nebraska and Wyoming. 

He is currently serving four life sentences without the possibility of parole in an Oregon prison. 

One of Jesperson's notes with a smiley face at the top

Keith Jesperson was nicknamed the "Happy Face" serial killer because he sent letters to the media detailing his crimes, which he committed across state lines as a long-haul trucker, with a smiley-face signature at the bottom of each note. (Okaloosa Sheriff's Office)

Picture of the side of the road where Claudia's body was found in August 1992

This is where "Claudia's" body was found in the city of Blythe, California, in August 1992. (Riverside County District Attorney's Office)

About two years ago, the Riverside County District Attorney's Office identified one of his victims – nicknamed "Blue Pacheco" after the color of her clothes – as Oregon mother Patricia Skiple. 

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Jesperson became known as the "Happy Face" killer because he sent letters to the media detailing his crimes, which he committed across state lines as a long-haul trucker, with a smiley-face signature at the bottom of each note.

In one taped confession, he told investigators, "After murdering too many people, it was just an easy thing to do," in a nonchalant manner, like he was describing how simple it is to boil tea.

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Anyone with information is asked to call the Cold Case Hotline at (951) 955-5567 or email coldcaseunit@rivcoda.org.