Police ask men in Truro, Massachusetts for DNA samples in murder investigation: Part 5

After three years of investigation into who killed Christa Worthington, the police finally made an arrest.
6:29 | 11/25/17

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Transcript for Police ask men in Truro, Massachusetts for DNA samples in murder investigation: Part 5
2002, Worthington homicide scene, truro, Massachusetts. Crime scenes are extremely important in figuring out potentially what happened, where did it start, where did it end, and what occurred in between, Christa's house is just a mess. There's things stacked. It's disorganized. Things are put away. If you don't know her and know how she lives, you would think that the bad guy has rifled through her stuff. She lived in a disorder that's almost impossible for you to understand. Her emotional life mimicked the way the house looked. It was topsy-turvey. There's nothing about this case that looks like this was a breaking into her house to steal things. This was all about her death. So, here's this murder scene and cheerios and a Sippy cup and little foot prints of ava's through the blood in the floor. Christa's vehicle, it was in the driveway. Her keys are outside. And some other personal items. There appears to be some sort of tussle or drag marks up to the door. The door was damaged, like potentially somebody kicked it. It tells you that there was a fight outside, and that she ended up on the ground, so there's a disagreement. It's very difficult without any eye witnesses. So, what you have to turn to in a case like this is the body itself. You're looking for some sort of evidence from beyond the grave. She's got some defensive wounds on her hands, and other places, suggesting she did put up a fight. She was stabbed through the chest, through the trapezius muscle to where the blade nicked the floor. The murder weapon has never been found, but there is a strong suggestion that the murder weapon was from her butcher block in her kitchen. What you try to do is sort of follow what you think the bad guy did. Where did he go? What did he do? What did he touch? They have problems here, 'cause this crime scene was managed very poorly. People have made lots of accusations about the crime scene. Police interviews, forensic tests. Peter Manso wrote about the investigation in his book "Reasonable doubt" The police here have not had to deal with a murder in maybe a generation, two generations, three generations, who knows. These people are not trained to handle a murder scene. A blanket was thrown over the victim. That contaminated the body. I can tell you one of the rules of protocol is not to take a piece of evidence from a crime scene and cover the body with it, even for decency's purposes. People were moving things around and touching things. The floor wasn't taped off for safe ways to walk on the crime scene. There was so many fingerprints from everybody touching everything. There's a huge difference between CSI and cape cod CSI. The district attorney Michael o'keefe told us first responders have to assess the threat and treat the injured. No crime scene is pristine. This one was better than many. While the crime scene was not pristine, they found critical evidence. DNA. Sperm and saliva. We believe that Christa Worthington was involved in an intimate relationship with a person prior to or relatively contemporaneous with her death. Investigators and Worthington's family say they hope the $25,000 reward they are now offering will help establish the identity of that person, presumably the last to see her. About that mystery man, the district attorney will only say he is not necessarily Worthington's killer. All we'd like is a resolution and some closure for Christa, and for her daughter ava. The police and the district attorney were desperate. They had not solved this case, so they decided to do a very unusual thing. Investigators took the controversial step of launching what's called a DNA dragnet. They asked all of truro's roughly 800 male residents to voluntarily give DNA samples. Who did the police question? Everybody. And they did so indiscriminately. So literally hundreds of people, myself included. The post office, the filling station coffee shop, and the highland grill are all locations in truro where police asked men this morning to use this kit and voluntarily give saliva samples containing their DNA. They approached you and asked to be able to swab you. Men only. Almost everyone in town was a suspect. I mean, have you ever heard anything so ridiculous in all of your life? I mean, it's like, are you kidding me? The reaction was swift. This DNA sweep is what catapulted the case to a national profile. A national debate invigorated. Police tried to find the killer by asking every man in a small town to submit DNA. Civil bibry were outraged. It wasn't so much to get the DNA, it was to find out who's reluctant to give it. The district attorney says investigators will look more closely at Tse who do not cooperate. I would just say to any member of the public that they should have no trepidation about cooperating with the police. This is big brother. This is 1984-type stuff. After three years of investigation, the police finally get this DNA break and they make an arrest, but they arrest someone that no one would have expected. We were stunned, especially since the person who was arrested was not anybody we had ever heard of. It's like he came out of nowhere.

This transcript has been automatically generated and may not be 100% accurate.

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