Juju Chang

You can hear the shotgun and then the line goes dead.

And in that last terrible moment of Heidi's life, investigators analyzing the call say they hear nobody else there but Heidi and Nick.

Next, the FBI is using new technology to reconstruct Heidi's final moments.

But even before they begin, there are plenty of red flags in Nick's version of the story.

He has a loaded shotgun and he is ushering Heidi down the stairs in front of him.

She's in front because I'm kind of trying to move her along quickly.

And then I'm right behind her.

Did that strike you as odd?

Yes, he's the one that has the gun.

Why does he let his wife go ahead of him?

They wanted to get out of there.

Still, it's just not making sense to investigators, so the FBI now brings in its forensic firepower to help.

The FBI came out and did a full kind of digital scan that didn't really exist in 2010 so they could make an accurate to scale digital model.

Nick tells in the interview about how the gun is sort of pressed up against his chest when it goes off and Heidi gets hit by it.

He's talking about the gun being chest high, and he says that, that they're fighting over the gun up here.

So how likely was that?

The FBI combines their ballistics testing with the virtual model of the space to find out.

They believe that shows that the gun wasn't at Nick's chest as he describes.

Instead, it was higher at his shoulder level as a shotgun would normally be if you're going to aim and fire.

Which makes them think this was a deliberate shot and not a shot that was taken in the middle of a struggle.