This episode contains graphic audio and references to self-harm and family violence.

Please listen with care.

I think that she is contemplating how to murder her family that night.

And she wants to do that for what purpose?

The sole purpose of greed, money.

When Detective Brian Beyerson first walked through the crime scene on Dean Drive in McLean, Virginia,

he saw a macabre jigsaw puzzle. And he wasn't yet sure how the bloody pieces fit together. But now, nearly 16 months

after the shootings, he was ready to make an arrest. Detective Byerson told me he believed

Megan started plotting the murders after her first failed attempt to wire money from her mother's account. And it may have all

come down to, as strange as it may seem, her mother's cell phone. That's how petty this whole thing is.

She knows that she has to have her mother's cell phone because she has to

answer that phone and she has to regurgitate a security number that they're going to give

her on that cell phone. And in order for her to get that phone, she's going to have to kill her

mom. That petty. That petty. But what about Helen? What motivated Megan to also shoot her youngest sister?

Perhaps it was to eliminate a witness even if it was her own flesh and blood.

I think Helen knew what happened.

I mean, I will never understand, I don't think, in any capacity,

why it is that Megan went upstairs and told her

that she had shot their mother.

I have no idea why she did that.

I can only assume that at some point

after telling her that she realized

...