I'm Lester Holt. Tonight on Dateline, a mother makes a promise to her son.

Keeping it will be the hardest thing she'll ever do.

I knew he was going to be out of the lake.

I'm calling and we're getting nothing.

Days and days putting out flyers and just searching.

Well, I can think about as I want James.

I'm pretty confident we've got blood spatter on the south window.

The last person to see him alive, that's a key.

Yeah, and I told you that proves that you loved the network.

He would post on Facebook different personas, homicidal highway.

He will morph to survive. Why is he in a Bible college?

I think I have a wolf in chief clothing.

So he's talking about shooting people before?

He's made it sound like that.

He's now seeing a young woman that terrifies me.

We did not even have a body in the case.

The evidence was not overwhelming.

You literally cannot stop thinking about it.

What keeps you going on these searches?

I'm a promise.

It's all I got left to give him.

And he's worth every mile.

...