Family of man convicted of killing Queens jogger insists he's been framed

Chanel Lewis was convicted of Karina Vetrano's 2016 murder in March. His mother told "Nightline": "He's not a monster as they want the world to know."
8:07 | 04/11/19

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Transcript for Family of man convicted of killing Queens jogger insists he's been framed
is speaking out about what she sees as a misjustice. We the jury find the defendant guilty. Reporter: Justice for Karina Vitrano, providing an end to a journey for her parents. Grieving can begin for us. Now my baby has justice. Reporter: She was young, beautiful, vibrant. Her life cut tragically short while she was out for a run in August 2016. Why did you kill her? Reporter: Lewis was arrested and charged with her murder. The jury deadlocked. Reporter: Months later, her parents hoping for a second chance to prove Lewis was in fact guilty to a new jury. But even in days before the second verdict, Lewis' fate remained uncertain. Cases generally don't get better with time. Reporter: Questions swirled around the validity of DNA evidence. You won't see channel's hair, body fluids. Reporter: Or whether his confession was coerced. A last-minute letter was submitted, questioning the investigation. But within hours, the jury was convinced, Lewis found guilty. There's no doubt in my mind, if the letter is confirmed to be authentic, and if the facts within the letter are found to be authentic, there are grounds for an appeal. Reporter: An appeal Lewis' mother Vida told us is coming. Her son, she says, is innocent, wrongfully arrested and framed for the murder. My son is not a murder. My son would never kill this young lady. The police department said they were confident he committed the crime. They believe my son is helpless. That's the reason why they chose him. Reporter: You are watching Karina's final moments, captured on surveillance video. You have a 31-year-old woman doing what women do all over the country, which is just exercise. Reporter: She went through this park but never came home. Later that night, her father says he went out in the dark with police officers, along this unlit jogging path looking for her. He found Karina's body just off the path. Myself, my family owe everything to the NYPD. Reporter: And six months later after no leads and no suspects, police would hone in on channel Lewis. We sent detectives to his house. He freely gave didn't a. Reporter: But his mother, accompanied by her ref rend and Christopher banks say the NYPD were pressured to bring someone in and targeted channel. That is a serious charge to law enforcement. We want to believe these are decent men and women who did the best they could and their evidence led them to your son. It's not a far stretch that this evidence was planted. Channel was perfect, perfect, perfect fit for this. He's not a monster. He's a god-fearing, loving, kind person. I understand her not believing her son did this, but there's so much compelling evidence in this case. Reporter: Chief Boyce was chief of detectives at the NYPD at the time of Karina's murder. What was his motive? Chance meeting. There's no way these two people would meet in life. Yet he saw her, was angry and attacked her when he saw her. Reporter: And that's what prosecutors presented at the first trial. In the retrial, the defense and prosecution would spar over key pieces of evidence, among them, Lewis' taped confession, which his defense says was coerced as part of a near 12-hour affair with a six-hour gap of Lewis not appearing on camera. People has to be in that courtroom to see that video. That's what they were doing, coercing my child, telling him what to say. Reporter: But Boyce says the video reflects how police interrogations should be conducted. You got to be honest. Reporter: Is there any chance one of your detectives could have fed him the information to misled him? That's why we tape our interviews. We do that for a reason, so people will believe us. Reporter: The prosecutors also zeroed in further on Lewis' DNA, key evidence cited in the trial which Boyce says was found not only under her finger nails but on her neck. A woman who's out jogging, of all the people in the universe, she could have bumped into channel while jogging? Absolutely, it can happen. And DNA experts say it can The DNA was planted, we Reporter: However experts say planting DNA is almost impossible. Altering the evidence held by the medical examiner or NYPD or a lab, the odds of that occurring in my view are beyond remote. Reporter: There is still the question of how Lewis became a suspect in the first place. Police say a lieutenant recalled seeing a man near the crime scene three months before the attack. So he saw this male, he saw him acting suspiciously. Reporter: His suspicions recorded in a 911 call played back in court. There's a suspicious walking back and forth around the block? Reporter: Lewis' family says that memory was too much of a coincidence and simply provided the perfect fall guy. There's pressure on the police department to find the person who did it. So what better person to look for than an African-American, black boy, who's helpless. It absolutely founds reasonable that a police officer would remember. You have to remember what the police do every day. Reporter: The final piece the Lewis family points to came in the form of an anonymous letter submitted to the defense in the final days of the trial, claiming there was indeed police misconduct. The letter claimed to be from a New York City police officer, saying in the first few days of the investigation, the suspects were two, quote, jacked up white guys from Howard beach. But then they found DNA information of a male black. I think it's an unethical attempt to disrail this investigation. Reporter: Based on the letter, the defense sought to exclude the taped confession and filed a motion for mistrial which the judge denied. My son would never assault this young lady. He has sister. He have nieces. Reporter: In a statement, the NYPD said they painstakingly investigated the murder of Karina, and as the prosecution demonstrates, the evidence clearly shows channel Lewis is responsible for her death. Although facing an uphill battle, his mother vows to continue to fight for what she believes to be her son's innocence. Have you ever spoken to the Vitrano family? No. But I give my condolences to the family, because I'm a mother also. Reporter: Yes, ma'am. And I know, I feel their pain. Reporter: If you could speak to them, what would you say to them? I would be very sympathetic. I sorry for their loss, but I will let them know that my son is not the killer. Channel Lewis will be sentenced a week from today.

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

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