On Saturday, March 10, Eric McLean shot and killed Sean Powell, his wife's former student and 18-year-old lover.

Natalie Morales: How often do you think about Sean Powell?
Eric McLean: I think about him a lot. I'm just really sorry about it. All of this. But I never wanted any of this stuff to happen.

No one involved in the fatal incident that night has given all the details about what happened -- including Eric McLean, whose attorney would not let him talk about the shooting itself. 

But after the shooting investigators pieced together clues.

Jamie Satterfield covered the case for the Knoxville News Sentinel and has seen key pieces of evidence.

Jamie Satterfield: Sean goes outside.  The evidence has suggested that he went outside, he got in his vehicle, he lit a cigarette, and he's sitting there.  And Eric goes out to his vehicle gets the rifle--
Natalie Morales: This is according to the evidence again.
Jamie Satterfield: Yes. And this -- this is the testimony from the investigator -- gets the rifle, and then fires it.  Um, and according to -- the medical examiner, what she classified as a defensive wound on his hand, cigarette still in--
Natalie Morales: Meaning he was--
Jamie Satterfield: Yeah.  That he would have reacted.
Natalie Morales: And he was not armed.
Jamie Satterfield: He was not armed.

Whether Eric McLean shot Sean Powell is not in dispute. He admitted it to Matt Lauer.

But right from the start, Eric McLean insisted it was not intentional.

Matt Lauer: Was this an accident?
Eric McLean: Yes!

Though he wouldn't provide details, Eric McLean's attorney, Bruce Poston, says he will prove the killing was unintentional.

Natalie Morales: It's an accident. Is that what you're saying?
Bruce Poston: I didn't say that. Those were Eric's words. But remember, they weren't just in the Matt Lauer interview. Those were the same words he gave to police in his statement. So that's twice he said the same thing.

Prosecutors didn't buy the accident theory.

Shortly after the shooting, police charged Eric McLean with first-degree murder, alleging Eric had planned the murder when he bought the rifle.

Natalie Morales: Why would Eric have a gun?
Bruce Poston: There's a lot of reasons people would have a gun … The state, they will claim he had it for at least 2 weeks, right? Well, why wasn't Sean Powell dead 2 weeks before? So clearly, he didn't get the rifle to shoot Sean Powell.

In late April, a grand jury indicted McLean for the lesser charge of second-degree murder. That means no pre-meditation. Now the most McLean can get is 25 years in prison.

Poston: They looked at the evidence and said no. The most we're going to let you try for is second. That was both a shock and -- and just a wonderful, wonderful surprise.
Natalie Morales: And how does this change the case?
Bruce Poston: It changes it dramatically.  This totally changes how this case is going to unfold. And it's much to Eric's benefit.

Jamie Satterfield: It puts the defense in a really strong position.  Because they're no longer trying to convince a jury that it wasn't premeditated.  Now they can really hone in on this notion that it's a crime of passion.
Natalie Morales: So what can we expect when it comes to a trial?  And how will this play out, in your view?
Jamie Satterfield: What you're going to see is a very pathetic-looking Eric McLean.  He's going to be teary-eyed the entire time. But sympathy doesn't cut it in the end when they're back there deliberating and looking at evidence.  And the evidence in this case is horrific.  The wound that he suffered his horrific.

Eric McLean's trial is now expected to begin next January. In an arraignment last month McLean's attorney said, simply, "It is going to be a war." And among the objects of his assault: Erin McLean and Sean Powell.

Natalie Morales: People are going to say, "How dare you blame the victim?"
Bruce Poston: I'm not going to blame the victim. I'm presenting evidence and the jury will come to their own conclusions.

Natalie Morales: You talk to anyone around town and you talk to the neighbors and everybody has an opinion about this already. And it's very unfavorable towards Erin. And it appears your legal tactic would be to make her out to be the villain.
Bruce Poston: I'm not going to try to make her out to be the villain.  She is the villain.