On a cool Saturday evening last March, the calm of a Knoxville neighborhood was shattered by a gun shot.

Erin McLean: My husband just killed someone!
911 operator: Is he there with you right now?
Erin McLean: No, but the body's here.

It was a wife's panicked cry for help.

Erin McLean: Oh my god! Oh my god!

Seconds earlier, a well-regarded husband and father, Eric McLean, had fired a single shot into the head of young man he'd described as an intruder on a 911 call.

Then he took off, leaving his wife Erin behind with a lifeless victim.

Erin McLean: Will you please come save him?
911 operator: Ma'am, they're already on the way.

But nothing prepared the community for what it would soon learn about the circumstances leading up to the killing.

The first hint of scandal was contained in Erin McLean's frantic call to 911.

911 operator: How do you know Sean?
Erin McLean: He used to be one of my students.

The victim was 18-year-old Sean Powell, and it would turn out Sean was no stranger to the occupants of 2424 Coker Ave. 
    
Sean Powell was born in 1988 to a single mom. He spent his early childhood in a loving home. He spent his first Christmas in a Santa outfit. His great grandmother was also a best friend.

But his mother had legal and financial troubles.  When he was six, she gave him up for adoption.

In Knoxville, Sean found a new life with another family -- the Powells -- and thought his birth mother had passed away.

But Debra Flynn searched for him, and when Sean was 17 they reunited.

Debra Flynn: Sean came down and grabbed me and hugged me and started crying. And he said, "Mom, I thought you were dead."
Natalie Morales: And what was life like when you reconnected with him? Did he tell you about any troubles in his life, tell you anything that was going on?
Debra Flynn: No, he just was happy.

Like many teenagers he liked to party to ride all terrain vehicles and to be on the athletic field.

Shilo Jines: Not to mention he played rugby but was poetic, too.

Shilo Jines dated Sean for a time last year. She says his passion for the arts -- for life -- was impossible to miss.

Shilo Jines: When you would look at him he would have fire in his eyes, he wanted to live his life to the absolute fullest, just every bit of it, the good, the bad, the ugly, everything … He wanted to just feel it.

At Knoxville's West High School, though, Sean had a reputation as a troubled student. He drank, smoked and was confrontational. In a class at West High last fall, he first met a student teacher.

Natalie Morales: When Sean was at West High School, did he ever tell you anything about an assistant teacher named Erin McLean?
Debra Flynn: No. Never.

Sean may have kept quiet about knowing his student teacher, but those who knew him say he bonded with Erin McLean right away over their shared interests in drama and poetry.

Shilo Jines: He was really intellectual and wanted to just experience and know about all he could … So she was really interested in things like him, so I could understand.

But Sean's days in Erin's classroom would soon come to an end. In October of last year, Sean Powell was expelled from West High just as he was turning 18.

So as he entered adulthood, he also seemed to enter a downward spiral.

Shilo Jines: Everybody had sort of worried about him just knowing that a lot of the time he threw caution to the wind. They'd always worried about him, but never, never could believe that something so absolutely awful would happen like this.

He spent several weeks in an alcohol rehab program and then told people he was kicked out of his home. The Powells deny that. Not many people were able to understand or help him, but Sean Powell thought he knew somebody who could.

Much of what happened is still very unclear, and as you'll see,  a Matter of he-said, she-said.  What is clear is that by last winter, 29-year-old Erin McLean and 18-year-old Sean Powell had begun a close relationship that only grew closer over time.  Erin McLean isn't talking. But it seems that over the next several weeks, that relationship became sexual in nature.

Around that time his former girlfriend, who stayed close to him, noticed a big change in Sean.

Shiloh Jines: Around January there was something different about him, it was different than the person I had met.

Whatever was going on, few seemed to know Sean Powell was involved with a former teacher.

Sean Powell's adoptive mother, Scarlett Powell, later gave a statement to the local newspaper saying she thought Sean's girlfriend was about 20 years old and a part-time student at a local community college. The name she had heard was Erin Myers -- Erin McLean's maiden name.

But looking back, Sean's birth mother says there were signs that something unusual was going on.

Debra Flynn: He wouldn't let me answer the phone. And I said, "Why not?"  and he said "Well, it's my girlfriend."  And I said, "Well, so?" and I had seen her number on my cell phone.  And he said, "Well, mom, she works at the school." And that's all. He wouldn't talk to me about it.

She did see messages from the girlfriend to Sean. "I love you," one said.  "Come home," said another.  Debra Flynn didn't pay much attention to them.

But two weeks later, that mysterious girlfriend placed a call to Debra Flynn's phone.  She said her name was Erin McLean and that she had some terrible news.

Sean was dead.

Debra Flynn: I said, "Who shot him?" She said, "This pyschopath" and I said, "Who's the pyschopath?" She said, "Eric" and I said "Who is Eric?" She said, "my husband."
Natalie Morales: Did you have any idea that Erin McLean was his former assistant teacher?
Debra Flynn: I had absolutely no idea.

Immediately after the shooting the story became a media sensation. A husband kills his wife's former student, her lover.

Tamara Mulkey: It was the shock of the century, because people like Eric you would never imagine them getting that point, ever.

Eric McLean was finally taken into custody the morning after the shooting.  He surrendered to police after dropping the rifle on railroad tracks outside of town.

He was charged with first-degree murder.

Erin McLean went to Nashville with her two sons. Then, a few days later, there was another call to 911.

Caller: A woman was, is attempting to commit suicide, she's taken pills, she's about to expire.

Erin McLean was apparently so distraught by the killing that a few days later she attempted suicide with non-prescription drugs at her mother's home in Nashville.

Then, some of the questions swirling around the case would be answered inside the Knox County Jail.

Just 10 days after Sean Powell's killing, Eric McLean sat down for a dramatic interview with Today's Matt Lauer:

Matt Lauer [co-host of "Today"]: And I'll ask you point blank: Did you shoot Sean Powell?
Eric McLean: Yes.

Lauer: You knew that she was having an affair?
McLean: I mean, I mean I pretty much knew. I think I was just, like, in denial for a long time, you know?
Lauer: Why not leave? Why not leave her?
McLean: I don't know. I just couldn't leave her.
Lauer: Explain that. Why not?
McLean: Because I love her!

But as you'll find out, that interview was just the beginning of what Eric McLean had to say about his marriage, his wife's secret affair, and what led up to that terrible night at 2424 Coker Ave.