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I stumbled back and I sat on the edge of my Jeep and caught myself with my hands. And in my right hand, I felt the metal from the garrote. It set me off. I just felt so much hate, so much rage. And I grabbed it and I stood up and I came up behind her and I put it around her neck.

Training took over then. Turned around and I started pulling. Nothing would have stopped me from doing what I was doing. I told myself while I was doing this, never again. I wasn't going to let anybody hurt my daughter again.

I had let her into my daughter's life. It was my fault that.

My daughter was hurt. I just kept choking her. I don't know how long it was. Might have been 5 minutes, 10 minutes. It felt like forever.

And I just kept choking her.

And then the anger, that feeling of disgust and hate, ebbed a little bit, and I let go. And she dropped to the ground. Christopher Lee was describing for the jury how he had killed Erin Corwin. After a few minutes went by, I realized what happened. I know I killed her.

And so the rope was still around her neck, so I grabbed it and I dragged her to the edge of the mineshaft and I pushed her in. His story accounted for all the physical evidence and portrayed the killing as a crime of passion committed by an outraged father. But now the prosecution took over and shocked the courtroom all over again.

Coming up, a heart-stopping moment. You could have stopped there, right? No. You couldn't have stopped? No.

The fate of Marine Corporal Chris Lee. What will the verdict be? When Dateline continues.

Chris Lee had shocked the courtroom telling the jury that he did kill Erin Corwin, but it wasn't premeditated. Instead, he said he snapped when he claimed Erin confessed to him that she'd been molesting his daughter. Now, Prosecutor Sean Doherty cross-examined Chris, confronting him on those allegations against Erin. I heard these accusations from your wife, who you loved, right?

Yes. So you immediately picked up and called the police? No. Nicole immediately picked up and called the police? No.

So you're still having sex with the woman who your wife thought was molesting your daughter, right? Yes. The prosecution's mission: show the jury that they could not believe Chris because he'd lied, claiming not to know where Erin was through all 8 weeks she was missing. People lie for a reason. It was important that I point out that he lies to protect himself.

You had a choice to tell the truth, right? I did. You knew Erin had a mother? Yes. You knew she had people that loved her?

Yes. You knew a lot of people were looking for her? Yes, I did. You essentially made the decision to hold them hostage, right? Yes.

Perhaps the biggest moment in court came when the prosecutor found a striking way to demonstrate how Chris had killed Erin. Okay, so for the record, what you do is you put it around the dummy's neck that I'm holding, you twist it around, and then you turn backwards. So you're actually back to back.

Back with her? Yes, sir. Okay. And you testified earlier that you pulled really, really hard. Yes, sir.

You could have stopped there, right? No, you couldn't have stopped. No, you already made the decision to kill. Yes. And you were going to follow through with that decision?

Yes. Okay. My goal was to show the jury how long it takes to kill somebody like that and to show them the brutality of what was done. It's one thing to say, as he did on, on direct, well, then I strangled her and I pushed her down the hole. It's another thing for him to actually show us what you did.

So I think the jury was entitled to see that.

It was heavy. It was one of the heavier moments I've had in court. That's about 10 seconds in. You could have stopped, right? No.

20 Seconds in, you could have stopped. No. Why not? Nothing would have stopped me at this point. I was too angry.

I saw the reaction of the jurors.

It was pained.

Their expressions were pained. So we're about 40 seconds in, you're still doing it? Yes, sir. That's about a minute in, still doing it? Yes, sir.