A big break in a cold-case investigation: It all starts in Marietta, Georgia, north of Atlanta, where a 3-year-old girl is the sole survivor of a horrific crime. For years she and police wondered not only who did it but why she wasn't harmed.

A mother and her teenage daughter were stabbed to death in their apartment in January 1986; the only survivor was a 3-year-old girl asleep in her crib. The victims: Forty-year-old Sharon Brady and her 13-year-old daughter Samantha.

At the time police issued a statement about the horrific crime: "Our only witness was a 3-year-old daughter who was in the apartment. We haven't really gotten a lot out of her."

The sole survivor is Brandi Marie Stone, now in her thirties. Her entire life has been haunted by the gruesome crime. Years passed and the case froze over.

Until one day, a sudden and unexpected break in the case.

Atlanta affiliate WGCL reports that a cold-case unit re-opened the files of the Brady murders. Luckily a few key pieces of evidence remained.

The man accused of slaughtering mother and daughter was already behind bars. Ronald Kyles was serving time in a Pennsylvania prison for aggravated assault.

So how was the cold-case unit able to identify Kyles as the alleged killer? His blood samples were already in the system, and so were the samples taken from the victims.

When the case was reopened, the forensics lab used today's DNA technology that didn't exist nearly 30 years ago to make a match.

A chilling detail is revealed: Kyles knew the Bradys; he lived just a couple of doors down in the same building.

Despite the tragedy that plagued Brandi, today the woman who lost so much has a full life with a family of her own.

Ronald Kyles will be extradited back to Georgia where he will face two murder charges.