I'm Lester Holt and this is Dateline.

You can lose a child without knowing it in a second.

It wasn't if it was a when are they gonna tell us that she's not coming home.

This is not what was supposed to happen.

The note was under her blanket.

I saw it sticking out and I grabbed it.

Their daughter was a runaway.

I am frantic because I didn't know how to find her.

They called police, they surced, and then a jogger found a red shoe and a pool of blood.

Here they are, three people at the door.

I just started sobbing.

They'd found her daughter, but not the boy she was with.

It was as if he'd never existed.

We couldn't find anything about LJ.

Months went by, still no trace of LJ.

And then a rookie took the case.

Had you feel about it that this was now going to be your case?

I didn't know if I was capable of doing this.

I cried for two hours.

A teen found dad.

We still don't have an answer.

A mysterious missing suspect.

...