She was murdered on her way to a bus stop. 40 years later, her case was solved

When leads in unsolved California killings stalled, one "badass detective" began pushing for answers.

Detective Matt Hutchison has spent yearsdigging intothe toughestcold cases to deliveranswers to families waiting for decades.

A new "20/20" episode,"Badass Detective," airing Friday, Jan. 9, at 9 p.m. ET on ABC and streaming the next day on Disney+ and Hulu, examines the cases.

You can also get more behind-the-scenes of each week's episode by listening to "20/20: The After Show" weekly series right on your 20/20 podcast feed on Mondays, hosted by "20/20" co-anchor Deborah Roberts.

One such case belonged to 15-year-old Karen Stitt from Palo Alto, who was murdered on her way to a bus stop in Sunnyvale in 1982, according to authorities.

Police found Stitt's nude body hidden at the base of a cinder block wall with her legs and arms bound by her own clothes, officials said. She was sexually assaulted and stabbedmore than50 times,and her personal items, like her makeup products, were strewn all around her, according to police.

Stitt's case remained cold for 35 years until Hutchison took it on in 2017, determined to find her killer.

"There was blood on the wall behind her body and then,up above her, there was more blood on top of the wall," Hutchison told "20/20." "It'scertainly the most graphic and violent scene thatI'veseen in my career as a police officer and firefighter."

Authorities used DNA to find a match in 2022. Gary Ramirez was living in Maui, Hawaii, but had resided in California at the time of Stitt's murder.

To find Ramirez, Hutchison and his colleagues used genealogical methods to winnow down Stitt's killer to one of four brothers. Then, DNAsecretlycollected fromone ofRamirez's daughters' trashcans in Southern California was testedto find the match.

In 2025, Ramirez pleaded no contest to first-degree murder in Stitt's death and was sentenced to 25 years to life in prison with a possibility of parole, which is the maximum sentence for the 78-year-old. Ramirez was not separately charged with sexual assault.

RobinMorris, Stitt's paternal aunt, told "20/20" thather niecewas a wonderful person.

"Karen was bright and kind and beautiful," Morris said.

Hutchison also began investigating a similar unsolved murder in Sunnyvale -- the 1979 stabbing of 18-year-old Estella Mena,ahigh-school student workingpart-timeas asecurity guard.

Mena was attacked in the office building where she worked, and her body wasleft in a corner next toa vending machine, according to authorities.

Using blood found on Mena's shoe, Hutchison found a genetic match in 2023. It was linked to a man named Samuel Silva, who had a criminal history of manslaughter, attempted murder, assault with a deadly weapon, rape and firearms offenses, authorities said.

Silvamay havemet Mena at a previous job at an amusement park,according to investigators, and he died in a Colorado prison in 2008, while serving time for a federal gun charge.

Despite his success in solving these cold cases, Hutchison acknowledged the psychological toll they take.

"They're going to haunt me. There's just no way around that. They get into your soul...and these cases will affect me for the rest of my life," the detective told "20/20."

Hutchison also acknowledged that he didn't solve these cases alone -- he picked up on work done decades ago.

"It was all of us. It's not just me," he said. "I was able to still test blood and clothing and different things and get DNA on them 40-plus years after the crime because the investigators collected them."