Transcript for Unraveling story of who murdered Darlie Routier's sons: Part 4
Darlie routier was charged with two counts of capital if convicted she could face the death penalty. My kids had been killed. My kids! I'm wanting whatever it's going to take to find out who did this. Darlie said there was an intruder, and I 100% believe her. I was in shock. I was completely blindsided. Just -- I couldn't even grasp what they were telling me, that they were saying I was under arrest for murdering my children. Darlie's trial had been set for the first Monday after January, so we had six months. I typically find that it's hard to be ready in a death penalty case in less than a year and a half. It was gonna be quick. There's no question. The crime scene tells a story, and it tells a hard story, and our thing is that story's not the same story that she's telling. Reporter: Skip Hollandsworth, a writer for "Texas monthly," followed the case closely. These are the notes I write in the early spring of 2002 when I first began to get involved in the case. Tons of interview notes, just to write one 6000-word for a story for "Texas monthly" magazine. One event with 100 different perspectives, and everyone has some theory about what happened that no one else knows. Detectives suspected that someone inside that home in Rowlett had killed the little boys. It seems clear that despite the fact that she was stabbed in the neck that investigators focused on her almost from moment one. So there were a number of things at the scene that led the investigators to believe that Darlie was the one who committed this crime. Is your name Darlie? Yes. Starting with that 911 call, there's a definite effort to classify Darlie as a non caring mother. One thing that investigators found very suspicious was a very odd comment that Darlie made on the 911 tape regarding fingerprints. His knife was laying over there and I already picked it up! It's all right, it's okay. God, I bet we could have gotten the prints maybe. My reaction when I heard that was just disbelief. She's got two kids dying in front of her. The thing that comes to her mind is fingerprints! Common sense tells me no mother would ever make a statement like that. The only inference we could draw was she was setting up why you're not going to find an intruders fingerprints on there. His knife was laying over there, and I already picked it up! When Darlie talks about grabbing the knife, it sounds suspicious, like she's trying to cover for herself. But the question is, did someone ask her a question about that knife? And that's the mystery. You know, they make a big deal on the 911 call. Darlie didn't say, oh, all this happened 911, and oh, by the way I've already touched the murder They left a knife laying on -- Don't touch anything. I already picked it up. Remember, the dispatcher just told her not to touch anything. There's a knife? Don't touch anything. When she said don't touch anything, it clicked in my head, you know, my gosh, I just touched a piece of evidence. The strongest evidence of innocent are the photographs of Darlie. In all the murder cases I've tried, I've never seen any self inflicted wound in the neck like that. I mean, just a fraction of a millimeter more and she would have bled to death. If you want to see a victim of a crime, that's the victim. She has a deep wound on the back of her right forearm. There are also cuts on Darlie's fingers of her left hand. This is typical of what you see in a struggle from trying to grab a blade and by somebody throwing their arm up to ward off a blow. That would be a textbook defensive type injury. Everyone agrees that Darlie had wounds, but prosecutors and defense see them very differently. Prosecutors believe she wanted to make it look like she had been attacked. It was a superficial wound. It just cut the skin. If you look at the injuries to the boys, deep stab wounds that went through their entire chest and back area. Because we don't have a live witness to contradict the story, what we're going to have to rely on is the physical evidence and the crime scene to do that for us. Another key item involves a broken glass. What she told the police was she woke up on the couch the man was standing over her and he attacked her on the couch. Darlie routier told the investigators that as the intruder was running through the kitchen, she heard a loud sound like broken glass. What's weird about it is that her blood is under that glass. Darlie's blood if anything should be on top of the glass; it's underneath. The problem is, every person that steps into that crime scene potentially contaminates it. Any crime scene like that is going to be chaos, because the first order of business is to save lives. So whatever they push or shove aside or step in that comes second. So using the position of the broken glass on top of footprints to conclude that it was an inside job and she had staged everything doesn't make sense. Another huge issue is the screen. We go back to the screen that's been cut by this supposed intruder. There's no indication whatsoever than anyone either entered through that window or exited out that window. The dust that's on that windowsill is undisturbed. If you assume that he exited out that window, he would've stepped very quickly into a flower bed with mulch on it. The mulch has not been disturbed, there's no footprints. Nothing to indicate that that area has been traveled through at all. The prosecution said that there wasn't an intruder here. They said that the window sill, you know, was not disturbed. 20 years ago Darin routier demonstrated why the states theory made no sense. Are you on? As you can see there's no mulch underneath this window, the mulch is at least 6 to 7 feet over in this direction and this is the window sill that they said was not disturbed. As you can see, you can walk right through this window without disturbing anything on the window sill. So the dust wouldn't have been disturbed, and there's concrete outside the window so the mulch wasn't disturbed. It's just silly. There are just a lot of nagging things about this case that do not make any real sense. We analyzed a lot of evidence. When you have a circumstantial evidence case, then it's all by the little pieces of evidence that prove her guilt. They say there's a staged crime scene, self-inflicted wounds. That there's a cut screen. There was the broken glass. The 911 tape. And it goes on and on, the number of things that sort of lead you towards Darlie. From the beginning, investigators themselves tended to focus almost exclusively on this quickly developed idea that it was the mother who did it, and that basically meant that they didn't ever have to go out and investigate alternative suspects. And so the question becomes, if Darlie didn't do it, who did? I saw this person's head turned, watching, just watching Darlie's house. I started to walk towards the car, and they pulled out very abruptly.
This transcript has been automatically generated and may not be 100% accurate.