SACRAMENTO (CBS13) — The murder of a Sacramento teenager remained a mystery for 25 years, until a determined detective made his move.

This is the story of a little girl lost, and the Sacramento detective who found justice for her. Twenty-five years after she was murdered, Penny Parker’s killer was found 2,000 miles away.

It was one of the first high-profile cold cases solved in the area, and how it happened is as fascinating as it is tragic.

Few pictures exist of Penny Jean Parker, but the memories of what happened to the 15-year-old girl are endless.

“She was always smiling, she was always happy, she was very friendly, she was always really nice,” said her friend Tammy Garrett.

The freckle-faced tomboy with a soft heart and a sweet smile was riding her bike one early evening in May 1977. near El Camino and Grove avenues in North Sacramento. Penny had a paper route delivering The Sacramento Bee.

On this evening, she rode through alleys where she played and down familiar streets collecting subscription money. She would never make it home.

Garrett will never forget the moment she was watching the news.

“I just remember the day they found her,” she said. “I just remember—I remember the room. I was sitting cross-legged on the floo. It’s embedded in my brain.”

Parker’s body was found three days after she disappeared near East Levee Road in Sacramento. She was discovered face-down in what used to be a cow pasture. It’s now Hansen Ranch Park.

The 15-year-old had been raped, strangled and stabbed. Video shot by Sacramento Police that evening still sends chills to those who were there.

The crime took Penny’s life and stole the innocence of so many who knew her, including friends and classmates at Las Palmas Junior High.

Thirty-eight years after the murder, Garrett still hurts for her friend.

“Every time I do anything, even now, and I think something happens and I think she never, ever got to do any of this, she never got to live,” she said.

She’ll also never be forgotten.

What mattered to Garrett was finding out exactly how Penny’s killer was brought to justice, and who helped solve the murder. She sent an email knowing the case was closed, but wanting to know more.

Pete Willover was the lead detective in the Penny Parker murder case. He recites what happened in 1977 as if it happened yesterday.

“It was around 5 o’clock in the evening that she had gone out collecting for the newspaper and then never returned home,” he said.

Out of thousands of cases, this is one that burned in his memory bank.

It was also a case he thought he had solved. Days after the murder, he immediately had his suspicions about the man who found her body.

“Our gut was telling us that something just didn’t fit and he very well could be the suspect,” he said.

Don Jennings was a known sex offender. He took a lie detector test and passed. With no witnesses, and no benefit of DNA technology at the time, Sacramento Police didn’t have enough to make an arrest.

“We didn’t have anything more to go on and the case eventually went cold,” Willover said.

It stayed cold for 25 years, until Willover went to work for the department’s cold case squad.

“Penny’s homicide, because I had worked it originally, was one of the first cases that we started looking at,” Willover said.

They hit a bull’s-eye.

“We did get lucky in the fact that we found her underwear and also some of the slides that had been taken at autopsy which contained semen,” he said.

From there, detectives got a DNA sample from a relative of Jennings, who always suspected he had something to do with Penny’s murder.

“It was like a 99 percent match and it gave us enough to go back get a search warrant in Arkansas and contact Jennings,” Willover said.

Arkansas is where Jennings had moved to, in a home near Hot Springs. Willover couldn’t get there fast enough.

“I interviewed him again and he still denied knowing Penny, ever having sex with her and stated that he just happened to come across her body and found her,” he said.

But the DNA swab taken from Jennings didn’t lie.

“It was a 100 percent match to the semen found,” Willover said.

Arkansas investigators moved in to make the arrest, but when they knocked on the door, they heard a gunshot. Jennings had put a shotgun barrel to his chest and pulled the trigger.

Penny’s family had closure. Justice was served by a determined detective who helped give Garrett the answer she was looking for.

“He didn’t even know her and the fact that she mattered that much to him that he kept on it after all those years—what a wonderful person,” she said.

“That was one of the main goals of the cold case unit was not only to solve these cases but to bring closure to the families of victims,” Willover said. “That’s why we do it.”

Had she lived, Parker would have been 53 years old this year. Her parents didn’t live long enough to find out her killer had been brought to justice.