Indiana police say cutting-edge genealogy and DNA techniques helped solve an infamous, 30-year-old cold case. Police arrested John D. Miller on Sunday and say he confessed to raping and strangling 8-year-old April Tinsley in 1988.

When they showed up unannounced at Miller’s home Sunday, detectives say the 59-year-old already knew why: April Tinsley. The 8-year-old vanished in April 1988 walking to a neighbor’s house.  Her body was found dumped in a ditch three days later; she had been raped and strangled, reports CBS News’ Don Dahler.

“If it wouldn’t have been for DNA, I don’t think we wouldn’t have gotten as far as we have,” April’s aunt, Teresa Tinsley, said.

The suspect left his DNA on April’s body and on threatening notes he used to taunt police 16 years later. Genetic genealogist CeCe Moore, who appeared in the PBS show “Finding Your Roots,” helped identify Miller as Tinsley’s likely killer.

“It’s exactly the same techniques that you would use for an adoptee to find their birth parents,” Moore said.

Moore and her team of DNA sleuths first uploaded the suspect’s DNA onto a public genetic database, GEDmatch.com, which found distant relatives in about eight hours.  From there, Moore built out family trees and then zeroed in on people who fit the killer’s age, physical traits and location. That process that can take a few days to a few weeks.

In Tinsley’s case, Moore determined her murderer was either Miller or his brother. On July 9, investigators secretly pulled used condoms from Miller’s trash and sent them to the state crime lab. Three days later, they got confirmation that his DNA matched the suspect’s.

“I really do appreciate the law enforcement agencies….Thinking outside the box, who have jumped right in and used this incredible technology to help bring closure to these families,” Moore said.

Since May, Parabon NanoLabs, where Moore works, has uploaded more than 140 crime scene DNA samples to GEDmatch and has gotten hits for more than half.

Genetic genealogy has already helped police identify suspects in five cold cases across the country including the alleged Golden State Killer, who is tied to dozens of rapes and murders in the 70s and 80s.

On the 30th anniversary of Tinsley’s death, her mother Janet revealed what she wanted to know most from April’s killer.

“The main question I would ask is why,” Janet Tinsley said. “What made her stand out the most? That’d be the main question I would ask him over and over and over again — why?”

Prosecutors will hold a news conference on Tuesday to give more details about how they identified Miller as their suspect. They have until Thursday to formally charge him with Tinsley’s rape and murder.