Lester Holt

We're joined now by Dateline producer Brad Davis, who has been working on this story.

Brad, good to have you here.

Great to be here, Lester.

Okay, so let's talk about the family au pair.

How does she fit into all this?

Yeah, Lester, she was the prosecution's star witness and testified on day one of the trial, which was sort of a surprise to have her testify so soon.

Her name is Juliana Perez Magalhães.

She's a young Brazilian woman who took care of the Banfield's daughter, Valerie.

And prosecutors say she and Brendan were lovers, that they wanted to be together.

And according to prosecutors, that's why Brendan came up with this elaborate plan to murder his wife.

And she told the jury that she helped Brendan lure Joseph Ryan to the home.

Explain how all that went down.

That's correct.

According to Juliana, she and Brendan did something called catfishing, which is where you pretend to be someone you're not online.

The au pair, Juliana, said that they went on a fetish website called FetLife.

and posed as Christine, using her pictures to invite Ryan over for a sexual liaison.

Then, when he got to the house, Brendan and Julianna shot him.

The defense said her testimony is not credible, and she's telling the prosecution just what they want to hear in exchange for a more lenient sentence for her own role in the murders.

Okay, so let's talk about the defense.

Over the past week, they've said that there just isn't enough evidence for the catfishing theory, and they called a man named Brendan Miller to the stand to talk about that.