Juju Chang

That was the single most important piece of evidence that I thought we had in this case.

Sipes now brings fresh perspective to a number of red flags that original investigators had noticed.

Heidi's only dead a few hours.

And for the most part of this interview, Nick isn't crying, isn't emotional.

I know she was hit in the back.

It was high in the back, probably.

Like up towards the shoulder blades?

I think so.

How worried was he about his wife during that interview?

He wasn't.

I just want to know the final answer on Heidi.

This is, you know, there's a couple parts of my job that I really hate, and this is one of them.

At that point, Nick does appear upset.

Still, Nikki Sipes says there's something important she never sees.

Nothing.

Sergeant Sipes then turns to the FBI to help her with Heidi's unsolved murder.

We were initially contacted by Detective Sipes from the St.

Paul Police Department to help with some audio from the 911 call that they had.

We really wanted to hear if you could hear this fictitious intruder.

The FBI took the audio recording to our laboratory in Quantico.