You can't believe that your baby's lying there and lifeless.

She was everything to me. She was so sweet to everybody.

State troopers said Bonnie had died in a hiking accident.

They said she fell off a cliff. Her mother said they were wrong.

I'm screaming to them. These are defensive wounds.

No witnesses, no weapon, nothing left behind, but a stranger's DNA.

I longer have some accidental death. This was a homicide.

They had no suspect, but for years her mother kept fighting to find Bonnie's killer.

Bonnie's mother continues her own crusade.

Then, after more than a decade of searching, a phone call.

They just got information. It was a match.

Can we get a conviction on just the DNA?

And there was something else, something about Bonnie herself.

It was almost like she knew something.

Good evening and welcome to Dateline. I'm Lester Holt.

We often see headlines about DNA evidence exonerating the innocent.

It seems we hear less about how DNA is used to track down the guilty.

In the story, a sample found on a murdered young woman was sent to the national database.

12 years after she was killed, it turned up a match.

One profile out of 5 million, matching a man, thousands of miles away.

But in this case, prosecutors would need more than DNA to convict a killer.

Here's Keith Morrison. Many years ago, laid on a September night.

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