The detective had found the missing Tara Grant, but only a part of her, just the woman's torso in a plastic storage bin inside the garage of the home she shared with her husband and two children.

Det. Kozwloski: I’ve never seen violence like this.

Alicia, Tara’s sister, had returned to her home in Ohio by the time the awful discovery was made.

Alicia Standerfer: And my phone rang about 11 pm and it was Sheriff Hackel and he said Alicia, “Do you feel like Steve would ever harm you?”

Watch the broadcast 'Valentine's Day Mystery' videos   Part 1: Wife goes missing   2: Detectives are thinking foul play   3: Police make gruesome discovery   4: The manhunt was on   5: Grant: 'And I choked her'   6: DA: 'It was about sex'

The sheriff didn't tell Alicia that they'd found her sister. But he was concerned for her well-being because Grant was on the loose. He insisted that she come back to Michigan immediately.

Alicia Standerfer: And I said,”Mark, I said, it's 11 o'clock. You want us to drive to Michigan. We have two small children?” He said, “Yes.”

Dennis Murphy: For your safety?

Alicia Standerfer: “For your safety."

At the sheriff's office the next morning, Alicia heard the incomprehensible news:  her sister, not only murdered but dismembered.

Then she had to tell her parents that their first-born was gone.

Alicia Standerfer: I don't even know what I said other than -- 'Tara’s dead, Tara’s dead.’

Stephen Grant had simply walked away before Detective Kozlowski discovered the torso. Now a day later the investigators were getting some good clues on his whereabouts.

Information pinging off cell phone towers told them that the cell phone Grant was using was headed north. They'd learned he was in a yellow Dodge Dakota truck borrowed from an unsuspecting friend.

Then a thoroughly unexpected and enormous break. The detective's desk phone rang.

Kozlowski: I recognized it right away as being an international call.

At the other end was a voice saying this is Verena Dierkes. Verena, the Grant's former au pair calling from her home in Germany.

Kozlowski: She was crying. And I had the sense to reach for my recorder and record the conversation.

(Audio from the taped Verena call)

Verena: Everything he said was a lie. Everything. And I believed everything.

And for the next 30 minutes what a story she had to tell. Verena, in the middle of the night for her, was saying that Grant had just called her and confessed to killing his wife.

Verena: He told me it was an accident … he said, 'She smacked me and she yelled at me and I pushed her back and she banged her head and was dead.'

The 19-year-old Verena swore to the detective that she'd always believed Stephen’s story that his wife had walked out. She had no idea, she said, that he'd actually killed Tara and the detective told Verena he believed her.

But he gently confronted her about stories told to him by the au pair's friends in the Detroit area. Rumors about her and Grant.

(phone conversation)

Kozlowski: Is there anything you want to tell me about your relationship with Steve?

Verena: There is nothing.

Kozlowski: You're absolutely certain about that, Verena?

Verena: Yes.

Interactive Photos: Remembering Tara Tara Lynn Grant was "a family-driven, career-driven woman," says her sister Alicia. Dateline NBC

Gradually, the cop coaxed the truth out of the teenager, bit by bit.

Verena: We liked each other. We liked each other more than we should. And it started about four weeks ago...

Kozlowski: How did it start?

Verena: I don't know. It -- it was just talking ... I don't know what -- maybe 'cause Tara was always gone. And then it was ... Just happened ... but it was never physical. Never. On that I swear.

Challenged on that point, Verena admitted a little more.

Verena: We kissed, but that's all.

And then, after further probing, she admitted a lot more: she'd had oral sex with her employer.

Verena: But it was just one time ... And it was before that happened to Tara. It was before the -- February the 9th.

Kozlowski: OK, was it mutual oral sex or just him?

Verena: It was just him.

Was Kozlowski hearing motivation for the murder? Did Stephen Grant kill his wife so he could be with the cute young nanny who was so good with the children?

Meanwhile, the intense manhunt for Grant was still very much ongoing and Verena provided the detective a solid lead. She told him Grant's call to her had registered on her caller ID as coming from the 989 area code, a big chunk of northern Michigan.

Verena was certain he intended to kill himself.

And in yet another call from Grant that night, this one to his sister near Detroit, he even gave the name of the remote cabins where he intended to take his life. The sister called the detective.

Kozlowski: So I basically Googled it. And it showed up Wagashantz State cabins in Wilderness State Park in northern Michigan.

Quickly, police found the abandoned yellow truck, followed the footprints in the snow and there under a tree, at 6:30 Sunday morning, was a dead-tired Stephen Grant suffering from hypothermia but very much alive.

Dennis Murphy: Do you think he was trying to kill himself?

Kozlowski: I personally think it entered his mind but when it really came down to it he lacked the courage to do it.

A Coast Guard rescue helicopter was called to the scene to reel in Grant and deliver him to a hospital.

He may have been exhausted but Stephen Grant still hadn't tired of talking about himself. He was about to tell everything.

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