Before we get started, we wanted to let you know that today's story had some graphic-disturbing content

about the violence but also sexual assault. With that, here we go.

Faisal, tell me this first. You walked into your house and the one.

When I jumped out of the cover here, I thought, before she could duck screaming,

I was like, towards that hair that would have the cord.

It was afraid for a while they might never find who did it because this is not television.

These things don't happen overnight.

She tried to fight you, you'll keep paying up. She finally passes out.

Just because it passes, don't mean this is.

I'm Scott Weinberger, investigative journalist and former deputy sheriff.

I'm Anna Siken-Nikolazi, former New York City homicide prosecutor and host of investigation discoveries,

crew conviction.

And this is Anatomy of Murder.

Today's case takes us behind the walls of a highly fortified military base and straight into an NCIS investigation.

It's a rare view into the Naval Criminal Investigative Service.

And for today's story, I spoke with Cynthia Snell, who herself served honorably in the US Marine Corps.

But it's the death of her daughter Amanda, a petty officer with the US Navy,

that would have NCIS investigators scrambling for answers.

In 2009, Amanda Snell was 20 years old.

She had been born on a marine base to a military family.

She was the brightest, the young lady that you would probably know.

She wanted to help everybody.

...