MATTHEWS, N.C. -- A Matthews family is talking to a national audience about the aftermath of one of the most horrific crimes ever in Charlotte.

David Crespi is serving a life sentence for murdering his twin daughters two years ago. Friday night, he and his wife are the focus of a report on ABC's 20/20.

Kim Crespi talked with Eyewitness News reporter Jim Bradley about her continuing struggle.

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Kim Crespi is still haunted by the murders of her twin daughters, and two years later, she’s still a defender of their killer, her husband. David Crespi stalked 5-year-olds Samantha and Tessa through their Matthews home and stabbed them repeatedly with kitchen knives.

“So why did Dave do that? Dave was not diagnosed bipolar on the day of the tragedy. He was also medicated inappropriately for a bipolar person. Why don't we talk about that?” Kim Crespi asked.

Crespi said she's frustrated that few others are willing to question whether doctors and anti-depressant drugs share the blame for David Crespi's violent rampage.

Crespi had suffered from depression for years. In a confession to police, he admitted having dark thoughts, which Kim Crespi believes spiraled out of control in a psychotic episode days after a change in medication.

“I think these dark thoughts were at a very specific time when he was adjusting to medications, and that's a key point that doctors should be telling people,” she said. “That when you're adjusting to medications, you can be propelled to act on your deepest darkest nightmares, and that is what David did.”

Until now, Marsha Goodenow, the chief homicide prosecutor who put together the case that sent David Crespi to prison for life, has not spoken publicly about the murder or the suggestion that Crespi wasn’t fully responsible. She said she speaks for many who believe no excuse excuses the murders of two innocent children.

“He was also asked, ‘Did you have these thoughts when you were on the medication or off the medication,’ and he said 'both,'” she said.

She described some of the horrific details of the slayings of Samantha and Tessa.

“Thirty-two stab wounds between the two girls. One of the girls still had the knife in her chest,” she said. “You can't say that someone who would do this to their own daughters isn’t sick. Obviously he's sick, but sickness does not excuse criminal behavior.”

“She's looking at this completely criminally and holding him completely responsible because he wasn't insane in the eyes of the law,” Kim Crespi said.

“And if she says he did hold the knife, he was responsible. You say what?” Bradley asked.

“I say she's right, he did hold the knife. I don't think he's solely responsible,” she said.

Crespi said she places forgiveness at the center of each day. She visits her husband in prison every Saturday and she still lives the rest of the week surrounded by pictures of her twins, living in the same house where they were killed.

She admits friends have fallen away and family has urged her to move on. But she’s telling her family’s story on national television, hoping to spur a national dialogue on mental illness and criminal justice.

“It's not that the criminal justice system is wrong for everybody. It's wrong for mentally ill people. If you don’t look at that you're not getting the full truth. And it's going to happen again and again and again and again, and so that's why we talked to the national media,” she said.

David Crespi will continue to spend his time in prison, and Goodenow said she will sleep well believing she's kept society safe from him.

“Nobody saw this coming, so nobody's going to know if it’s coming again,” she said.

As for Kim Crespi, “Somehow I wake up every morning and the nightmare is still happening. But I feel like I can make a difference, and if I died with just that feeling, that's OK because at least I've tried,” she said.

Despite her critics, Kim Crespi said she'll keep beating a drum of forgiveness not everyone wants to hear.

You can see more about the Crespis, including a prison interview with David Crespi on 20/20 Friday at 10 p.m. If you miss it, you can watch it online by clicking ABC News on Saturday.