SCOTTSDALE, Ariz. - Police have arrested a Phoenix man in the death of a 31-year-old woman found beaten to death in her Arizona home three years ago. Her death is the first mystery to be solved by Arizona police through the use of familial DNA testing, a controversial emerging technique, officials say.

Allison Feldman, a 31-year-old medical sales rep originally from Minnesota, was killed in her Scottsdale home in 2015. Investigators said she died of blunt force trauma. Her boyfriend reportedly came home to discover her body.

A police probable-cause statement says detectives identified 42-year-old Ian Mitcham as a suspect because his brother's DNA is similar to a profile of DNA evidence found at Feldman's home and that Mitcham's own DNA then was found to match the crime-scene evidence. The brother was already in the prison system, CBS Minnesota reports.

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Mitcham appeared in court Wednesday and remains jailed in lieu of $5 million bond on suspicion of first-degree murder and burglary. According to police, Mitcham denied knowing Feldman or having been in her home.

It's unknown whether he has an attorney who could comment on the allegations.

"It's been very overwhelming. It's kind of hard to believe this just happened," Feldman's sister Kelly Weinblatt told CBS Minnesota reporters.

Weinblatt said she's always kept hope alive that police would find the person responsible for killing her sister, but that it had grown more difficult as the years passed.

"We exhausted, over that three-year period, every lead we had," Asst. Chief Scott Popp of the Scottsdale Police told reporters Tuesday.

Popp said the department is now "100 percent certain" that Mitcham killed Feldman.

"Certainly knowing that he's not walking the streets and living his life is somewhat comforting to us," Weinblatt said.

The family will be flying to Arizona for the court proceedings, according to the station.

Familial DNA searching has made inroads in some U.S. states and other countries in the last decade, leading to high-profile arrests, but has also caused controversy amid civil-liberties qualms. Critics view the technique as a DNA dragnet that can single out otherwise law-abiding people for scrutiny because of family ties.