Transcript for Former lover, father of child was once a suspect in Worthington murder: Part 4
My darling daughter, I am interested only in your welfare, only in you. Reporter: In her diary, Christa talks about her adoration and her love for her baby, ava. We took you to the ocean today, it was the waves! You are so brave and zoom straight for the water fearless and joyful. She also feels tremendous resentment towards ava's father, Tony Jackett. She feels abandoned by him. I get so upset that that creep is her father. %-Phow he has let me down. Reporter: They decided that they would tell no one about the baby, but when ava is about a year and a half years old, Christa demands that Tony tell his wife, Susan. The baby got to an age where she started to talk and was about to start asking questions like, "Where's dad?" And that's when she wanted me to tell my wife. I was totally devastated. I was so shocked. He never wanted to leave. He was never unhappy. He was just a naughty boy. Susan, god bless her, welcomed Christa and ava into their lives. Reporter: Tony and Susan and Christa would have Sunday dinners together, and the theme of this was "Let's give ava a home." She wanted to develop a relationship with little ava, knowing this is her husband's daughter. The last time Christa is seen alive for certain is in a surveillance video from a stop and shop Friday afternoon. We see her with her daughter, ava, pushing a cart. It's always eerie, sad to see video of a victim in the last moments of the person's life. Little did she know that within a day she would be dead. Christa Worthington, found stabbed to death in her truro home. Her then, 2 1/2-year-old daughter clinging to her lifeless mother. George Malloy was one of the first medical personnel, emt, to arrive at the scene. Most importantly, he's the one who has to comfort ava. I just sat down and tried to communicate with this little girl. I didn't know whether she had witnessed her mother's death or what had gone on. I was asking her when was the last time you were changed? When was the last time you had anything to eat? There was no response really. Different people started to show up. Tony's wife and Tony showed up. And Jackett's wife said to me, you know, "Don't listen to anything this little girl has to say, she's a Liar." And I'm thinking to myself, "What the ?" Susan says she never called ava a liar. She was making a lighthearted comment about her fibbing and that's been taken completely out context. At this point, you've got a dead woman who he's had an affair with. You've got his wife in front of me telling me that the 2-year-old is a liar. I suspected him as a suspect, the first suspect, and then her as the second. The investigators find a letter that Christa wrote to Susan about the affair. She never sent the letter in which she said, "When you thought Tony was taking your son to the bus station, he was Me. This was a letter written by one woman to another meant to hurt, to injure. From September to the day your mother-in-law died, I was sleeping with your husband. I thought you should know. The letter would definitely be important for police because they're going to be wondering if Christa was so angry at Susan, was Susan so angry at Christa? They asked Susan to take a polygraph test and she agreed and she passed. As the investigation turns towards Tony Jackett, the investigators realize that there may have been a lot of pressure on Tony Jackett. She wanted him to help her bring up this child, putting her on his health insurance and providing financial support. She got herself a lawyer and said, "You're gonna support this kid or I'm gonna sue you." Maybe Tony wanted to get Christa out of the picture so he could just take ava and raise her himself. Why would I want to kill her? But, they're getting information that says otherwise. That Christa wanted money, that Christa was gonna go back to court. At the same time of the murder investigation begins, Tony has a custody battle. Amyra chase was Christa Worthington's very good friend. Christa had a will and in it she named amyra guardian of little ava. She is like a light in our family. She's a beautiful little girl and we love her. The D.A. Was there. He had gotten up to speak. He said we can't rule Mr. Jackett in or out as far as being someone that could've committed this crime. He didn't want to put his family though even more pressure. So he stepped back and Amira stepped forward. The decision was that amyra was going to get custody. The investigation seemed stalled. So, what you do is you make the circle bigger. The state police drove down to New York to see Churchwell, the magician. They said, "Well, we feel that you did this." I'm like, "Why?" They said, "Well, because it's something that a magician could do. He could create this mystery." I said, "Just because you can't figure it out does not mean that it was a magician that did it." There were so many different possible suspects. This case almost becomes like a game of clue. Even Christa's father and his girlfriend were potential suspects in this case. Christopher toppy Worthington, 72-year-old harvard-educated lawyer, turns out had a 29-year-old girlfriend who was a former prostitute and heroin addict. Toppy was taking money and supporting Elizabeth porter. The names on apartment are porter as in Elizabeth and Worthington as in toppy. On top of the social embarrassment of having her dignified, elderly dad cavorting around was the fact that she was watching her future share of the estate go away. She wanted this stopped. Elizabeth porter kept her hood up and her head down today. State police questioned her in the investigation of stabbing death of fashion writer Christa Worthington. Perhaps the girlfriend offed Christa as a way of continuing the gravy train. Interestingly enough, toppy and Elizabeth did not pass their polygraph tests. Unfortunately for the police, they had no evidence to link either one of them to Christa's murder. So now they keep looking. The police and the district attorney were desperate. They found no evidence that any of the people they had been investigating were involved in Christa's murder. Every one of the initial set of possible suspects denied having any role in Christa's death. The pressure was mounting to bring someone in. No one elects prosecutors to have crimes remain unsolved. They turned to what many people call a forensic hail Mary. Investigators took the controversial step of launching what's called a DNA dragnet. I mean, it's like, are you kidding me?
This transcript has been automatically generated and may not be 100% accurate.