By 2007, Barry Beach had been behind bars in Montana for 24 years. Now, after a decade of work, investigators from Centurion ministries had come to a conclusion: even though Beach confessed to killing Kim Nees back in the summer of 1979, he was, they believed, an innocent man.

Jim McCloskey, Centurion ministries: We have not developed any information that would tell us, hey, maybe Barry’s guilty. Because if we did, I can assure you that Centurion ministries would have dropped this case years ago and moved on to more fertile fields.

Keith Morrison, Dateline NBC: I can see the state saying you guys are just trying to be heroes at the expense of justice.

McCloskey: We're not afraid of admitting we made a mistake. We've done it before, we'll probably do it again. But in this case I don't have any information that says we're wrong.

But it was the secrets in this old town that persuaded Centurion it had a different kind of case, that it was able to say not only that Barry Beach was innocent, but that it knew -- or thought it knew -- who might be the real killers. For 25 years the rumors had persisted that a group of girls killed Kim Nees. And now Centurion investigators encountered more than just rumors.

What did Centurion have to point to a group of killers?

Remember, the prosecution theory and Barry Beach's confession was that Beach alone killed Kim Nees at this popular party spot about a half-mile outside town near the Poplar River, sometime after 1:30 in the morning on June 16, 1979..

But listen to this witness found by Centurion: a rancher who says he saw Kim Nees’ pick-up at 2:30 a.m. heading out of Poplar, toward the spot where she was found dead just hours later.

Holen: What I remembered the most about it is the pickup was so full people.

Keith Morrison: Could you tell if they were boys or girls?

Holen: No, but I mean it was just full of people.

The state claims the rancher has changed his story since the days after the murder.

Keith Morrison: Could it be a false memory, do you think?

Holen: No, I can see it.

And that sighting about 2:30 a.m. is key, says Centurion, because listen to what two more witnesses say they heard at that time from the area where Kim Nees was killed.

Jim McCloskey: What do we have that illustrates that she was killed around 2:30? We have Joel Sparvier and his mother overlooking the park. He hears screaming. His mother hears somebody yelling “help me, help me!” Screams, a high pitched female voice coming from the park.

Could they have heard the murder being committed?

Next, Centurion's investigators found a rancher who says he got a phone call just a couple hours later, before dawn.

O’Connor: It was from a lady by the name of Sissy Atkinson.

Sissy Atkinson is a name to remember.

O’Connor: She proceeded to tell me that they found Kim Nees’ body down by the train bridge.

Keith Morrison: What did you think when you..?

O’Connor: How does she know?

How indeed? Especially given the hour…

Keith Morrison: What time was it?

O’Connor: Around five o'clock.

Five a.m.? How could anyone know that a body had been found two full hours before the police discovered it?

Keith Morrison: Did you ever tell the authorities what had happened?

O’Connor: I might have mentioned it to the county. But I think it went in one ear and out the other, especially after they rounded up Beach.

Then there was this: Centurion's investigators found a man who said years later, he'd overheard Sissy Atkinson making incriminating statements in a factory where they both worked.

Carl Four Star: She was talking about the Kim Nees murder and how the wrong person got put in jail.

Keith Morrison: What a strange thing to hear.

Carl Four Star: It gave me the creeps you know, and as she walked by she looked at me and she said “We got away with the perfect crime.”

Keith Morrison: She said that to you?

Carl Four Star: Yeah, I just said “you stay the hell away from me.”

And finally, there is one more person who claims he heard Sissy Atkinson talk about the murder. It may be the last person you'd think would ever come forward.

This man's name is J.D. His last name? Atkinson. Yes, he’s Sissy Atkinson’s brother.

J.D. Atkinson: I think Kim Nees is looking over Sissy's shoulder all the time...

During a visit to Montana State Prison, where he was serving time on drug charges, we asked to see him. We asked if he had any information about the murder. To our surprise, he said yes. The story goes this way, says J.D. One night he and Sissy were talking, and she was high.

Keith Morrison: Did your sister Sissy tell you that she was there the night that Kim Nees was killed?

J.D. Atkinson: Well, the way she said it was that they were partying down there…

Keith Morrison: And there were other girls there too?

J.

Video   'I would never have hurt her' Barry Beach says he is innocent in the death of Kimberly Nees. Dateline NBC

D. Atkinson: Yes.

Keith Morrison: How much did she get out before she dropped off?

J.D. Atkinson: Just that one of those girls came running around the truck with a crescent wrench.

Remember, the medical examiner said at least one of the weapons that killed Kim Nees was likely a crescent wrench. But J.D. Atkinson said his sister passed out before saying any more.

Peter Camiel: One of the things we keep hearing from the state is that these girls, if they were involved, wouldn't have kept quiet. Somebody would've heard something over the years. And these people who have come forward did hear something. And they didn't keep quiet. And that's why it's important.

But after all these years, does it really add up to new evidence?

Keith Morrison: All you have is just a lot of hearsay evidence that says the hearsay evidence about Barry isn't really very good.

Jim McCloskey: We claim it's not hearsay when you have Sissy Atkinson confessing to being one of four girls who are killing Kim. That's not hearsay, that's a confession.

We wondered: what would those girls named as suspects by Centurion in this long ago murder have to say about all this?

You're about to hear their side of the story, for the very first time.

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