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KANSAS CITY, Mo. — Thirty one years after her murder, a Kansas City family finally has answers as to who killed 16-year-old Fawn Cox.

On Monday, Kansas City police and the local FBI field office said the case was solved using “advanced techniques.”

“It was our honor to notify her family of this news today, and we hope they might finally have some closure after decades of uncertainty and pain,” police wrote on Twitter. 

Family said they were told the killer was a cousin, 21 at the time of the murder, who died in 2006.

In the summer of 1989,  Cox was sleeping in her upstairs bedroom on E. 9th Street. Someone broke in and raped and strangled the teen, all while her family slept downstairs. An air conditioner unit muffled the sound.

“She was my protector. She stood up for me,” her sister Amber Gonzalez said.

Gonzalez, just one year younger than Cox at the time, has always hoped police would find the killer through DNA evidence. In the 30 years since her death, that evidence had only been used to clear a neighbor and three juveniles, who were originally charged. 

In March, investigators told FOX4 they were working with federal partners to secure money to do genealogy testing. Everyone who goes to prison automatically has their DNA uploaded to the Combined DNA Index System, known as CODIS. But forensic genetic genealogy testing has proven successful in cases like California’s Golden State Killer.

“I don’t know how to explain it. It’s the happiest moment. I can’t be nothing but happy. This is what I’ve been praying for for my family,” Gonzalez said. 

Police said the recent investigation was complicated by the fact the killer died in 2006. Gonzalez said she was surprised it was someone so close to them.

“That had to take a lot to be around a family that they murdered their child,” she said.

Now with Kansas City’s first case solved with the new advanced techniques, she hopes it won’t be the last.

“It’s not only about my sister. There’s a lot of people out there that wants this, too,” she said.