3 a.m. knock at my door. They said your dog's been shot and he's been killed. I screamed.

The scariest thing that you'll ever go through. My whole world crumbled.

Cara was the kind of teacher that students just love. She was a rock star at her school.

With the same man for 20 years, enjoying life together by the beach.

The balcony was like our second living room. You can hear the waves on the shore.

But she was all alone that night. When she says an intruder burst into her bedroom.

I was scared to death. I didn't have any other choice.

You shot him? I shot him.

She said the man attacked her. He told me he was going to kill me.

She'd been assaulted. She defended herself.

So why did others call it murder?

My very first words were she set him up.

Cara's account kept changing.

It hit me just how different all of these stories were and how unbelievable they were.

Lies. It's all lies.

What really made Cara pull that trigger?

The rug was pulled out from underneath her. She was shot.

And she was angry? Yes. A jury would have to decide.

I did what I did because I had to. Not because I wanted to.

In this story, the killer was never in doubt. It was motive. That was the mystery.

I'm Lester Holt and this is Date Line.

Here's Keith Morrison with a shot in the dark.

...