God knows, please, no.

This can't be real.

A teenager, home alone, in a night of terror.

I would just stare at the windows and try and figure out how scared she was to be at this.

On her body, like a signature, a handprint in blood.

It was a crime of passion.

There was a lot of anger involved in this.

But hang on, because that handprint doesn't belong to the man police put in prison.

The anger just surged through me.

Now, a mother turns detective.

Her words to me, I'll never forget were, I just want to know what happened to my daughter.

Join in as she hunts for a killer and searches for the truth.

I wanted to put my fists through the TV.

It still brings the hair up on the back of my neck.

The confession.

Welcome to Dateline, everyone.

I'm Lester Holt, a police interrogation videotape.

It can play a big part in any case, but rarely the way it does in tonight's story.

For the mom you're about to meet already grieving for her dead daughter,

the tape revealed something almost as shocking as the murder itself.

Here's Keith Morrison.

They kept him in the Idaho Correctional Center, deep inside the multiple walls and the armed doors,

...