Nightline, a mothers reckoning, will be right back. This is a special edition of nightline, a mothers reckoning. Good evening and thank you for join us. Tonight the powerful and untold story of the mother of one of the columbine shooters. Nearly two decades later, sue klebold is speaking out. The mother trapped in contradiction between a little boy and all she believed he could be and the murderer he became. And especially for the families of the victims, those urgent and anguished questions never answered, until now. Constitute massacre have been prevented, and warning signs that may have been missed. Heres abcs diane sawyer. Reporter it is 1999. A shock wave hits america. Two High School Boys in trench coats carrying shotguns, a semiautomatic weapon, and homemade bombs walk into their school and begin the slaughter of their classmates. Who were sitting on the grass eating their lunch. Who were hiding under tables. No defense from the terror. 13 are kill the. 24 are wounded. And we are all watching for the first time children run out of their school fleeing mayhem. A lot of students coverage of the columbine reporter we see a wounded student struggling out the window of his high school to escape with his life. And for the years to come, we would all be asking the same questions who were these killers . And what kind of parents could produce children like these . Someone wasnt doing their job. Reporter for 17 years now, the parents of Dylan Klebold and eric harris have lived their secrets, unwilling to step forward. Until a grayhaired woman makes her way into a room. In the course of this day at one point we see her pacing. Perhaps grappling with her decision to step forward after 17 years hiding from cameras. Years of being hated, threatened, she says afraid and ashame the. So klebold is now 66 years old. For the families of 13 people who died and 24 people who were injured, most of them children, what is it you want to say to them . The one thing, of course, that i want to say is, i am so sorry for what my son did. Yet i know that just saying im sorry is such an inadequate response to all this suffering. There is never a day that goes by where i dont think of the people that dylan harmed. You use the word harmed. I think its easier for me to say harmed than killed. Its still hard for me after all this time. Is that about a certain need to deny what happened . I dont know. Perhaps. Perhaps. Reporter she seems to be trapped in a contradiction. Remembering the son she once had and the murderer he became. Called him the sunshine boy . We did when he was little, yeah. He had this sort of a mane of golden hair. It was just thick and round and he was such a happy, precocious, brilliant little child. For all the parent hot have said, i would have something, i would have just known. I know. Before columbine lefthand side, i would have been one of those parents. And i guess thats why certainly why im here talking to you today. Reporter she has written a book called a mothers reckoning. In it she says all the lessons of her regret which began on the day she woke up an ordinary wife and mother, fast forward 24 hours and i was the mother of a hatecrazed gunman. She remembers the shocking prayer she found herself praying after learning her son might be one of the columbine shooters and the shooting was still going on. The police were there. The helicopters were going over. And i remember thinking, if this is true, if dylan is really hurting people, he has somehow he has to be stopped. And then at that moment i prayed that he would die. That god stopped this. Just make it stop. Dont let him hurt anybody. Reporter but by the end of the day, her son and his friend would take the lives of 13 people and then take their own. In her book sue klebold writes, her son wasnt the pinwheeleyed portrait of evil we know from cartoons. He was shy, like bible, handson parents, put them to bed with stories and prayers and hugs. Reporter sue klebold calls dylan her shiny penny. In gifted classes. Loved little league. Gave big hugs and kisses. Built tall ships out of legos. He wouldnt just work on one puzzle, hed dump them into a big mountain so he could solve five or six of them at the same time. Reporter she says he was easily embarrassed, tearful and hard on himself if he made a mistake. Shy heading into adolescence. He talked about looking weird . He was a tall, gawky kid with glasses. Reporter she says she does notice something, that dylan seems to be losing interest in good grades. But she now says, as she looks back over her life, she is male a big mistake. Her son is changing. But she writes off the changes. As an adolescent phase. Sometimes he would seem distant or quiet. And i remember asking him, are you okay . Are you sure youre okay . You seem so tired. And hed stand up and say, ive got a lot of homework, i need to go to bed. And youd let it go. I let it go. And thats the difference. I would dig. If it were me today, i would dig and dig and dig. Reporter she has no idea her 15yearold son has begun a secret journal. And his first entry is this. Thinking of suicide. I hate my life, i want to die. I have a nice family, good house, couple of good friends. No girls. Nobody accepting me even though i want to be accepted. But at this point we want to be very clear 80 to 90 of depression can be treated. And even suicidal depression is not an explanation for a pathway to violence. Dr. Gregory fritz wants to warn parents tonight that suicidal depression is real and can strike any teen anywhere. Somewhere between 15 and 20 of High School Kids say that they have thought about suicide in the past year. Reporter but more than 17 years ago, sue klebold says she knew so little about teen depression. Could you have prevented what happened at columbine . If i had recognized that dylan was experiencing some real mental distress, he would not have been there. He would have gotten help. Reporter in this video from his junior year he seems selfconscious but talks about the future, going to college. So you get better chances at high school as far as college goes, maybe a scholarship. Reporter around the same time, a series of troubling events. He hacks into the School Computer system with some friends. Theyre all suspended for three days. He scratches an epithet on the locker of a kid he thinks is taunting him. Then the big shock, he and another kid break into a van, steal electronic equipment, and police make an arrest. This is a felony, two felony counts. It was terrible, i know, absolutely. It was awful. And at the time i thought that was the worst thing i could ever possibly experience. Reporter dylans cold reaction after the arrest scared and shocked her. He acted as if he had done nothing wrong. She says she gave him one of her lectures, trying to reason with him. I even talked about the ten commandme commandments, its wrong to steal, in no circumstances this is right. And then we responded as most parents would. We took away privileges. Reporter one night shes frustrated, hes not doing chores, hes withdrawn, she pushes him against the refrigerator. I said, youve got to stop thinking of yourself, youve got to stop being so selfish. But excuse me. But i gave him the old mom lecture. And then i said, by the way, todays mothers day and you forgot it. And i dont remember how that confrontation ended. I just remember he softly said, mom, please dont push me, i dont know how much i can control myself. It wasnt a scary thing. It was just him being nice to say, back off, please. Reporter she says she blamed herself for pushing him too far. Then he went out and he got me a gift. A little it was a little water king with african violets in it. And i thought everything was fine. Because he was so he was so sweet. When we come back, the secret journals. What do they reveal about the minds of two teenagers responsible for columbine . And what forced sue klebold to finally face the truth about her son . Tonight, what experts tell us might prevent a tragedy. The setting is just right. Theres something in the air. But heres the thing about half of men over 40 have some degree of erectile dysfunction. Well, viagra helps guys with ed get and keep an erection. Ask your doctor if your heart is healthy enough for sex. Do not take viagra if you take nitrates for chest pain or adempas® for pulmonary hypertension your Blood Pressure could drop to an unsafe level. To avoid longterm injury, seek immediate medical help for an erection lasting more than four hours. Stop taking viagra and call your doctor right away if you experience a sudden decrease or loss in vision or hearing. Ask your doctor. About viagra. Available in single packs. 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Almost twothirds will be from twoparent homes. Nearly half of the kids will do well in school. 73 of them will never have been arrested before. And yet every child you see here will become a school shooter. In total murdering 67 people. The child in this picture is Dylan Klebold. I dont think he was always a violent young man. I think it evolved over time. I think it took a lot of time. Reporter we brought in former fbi agent mary ellen otoole, one of the worlds leading profilers of the criminal brain. She has analyzed thousands of pages of evidence on columbine and Dylan Klebold. You dont think School Shooters just snap one day . Absolutely not. I have not ever seen where that has happened. I think he was in a very destructive friendship which was very powerful. Maybe even more powerful than what we think. Reporter there is no way to continue telling this story without going back to another little face in that class picture. A friend who was with him breaking into the van. Eric harris. He would become the other shooter at columbine that day. He has also begun to keep a secret journal, and his journal is filled with venomous threats, graphic fantasies about revenge on people who have insulted him. People engulfed in flames, detap dated heads. According to otoole it signals a personality disorder, a psychopathic brain. These are people without a conscience. These are became without empathy, without guilt. Reporter is eric harris really different from Dylan Klebold . Another expert on columbine, dr. Peter lang man, insists he is. Eric liked to draw weapons, swastikas, wrote about the nazis. Dylan drew hearts. Dylan wrote about his search for true love. Eric when he does refer to girls, his fantasy is raping them. Reporter in their senior year, eight months before columbine, the two boys spent more time together. They liked violent movies and making little movies of their own. Trying on what its like to be tough guys. Eric is smooth. I think we might have to get some more weaponry. Reporter dylan stumbles. Its a good thing we uh we ordered those radio [ bleep ] reporter the camera shuts down. Eric writes, everyone is always making fun of me because of how i look, how weak i am. Guns, i need guns. Dylans and for one too. And i had told him no. Reporter sue klebold said she used to look through his room during his junior year, but by his senior year she decided to respect his privacy with distance and regret she now says how wrong that decision was. Would you ransack his room now . I would. Id do it as if his very life was depending on it. And i would do it with love. Reporter the boys were already getting their hands on guns and hiding them. A girl, a School Friend old enough to buy them legally, got them three at a gun show. She trained at a range. And Dylan Klebold writes, he now has a choice. Committing suicide or going nbk with eric. Nbk, naturalborn killers, the violent revenge movie by oliver stone. Which brings us to the central question about Dylan Klebold. Why did he go from suicidal to homicidal . Did eric infect him with a kind of pathological virus . Or was it dylans presence that reinforced erics violent fantasies . Do you think Dylan Klebold knew right from wrong . Yes, absolutely he did. But it did not preclude him from being able to participate in the planning and to carry it out. Do you believe in evil . I dont think so. I dont think i do. Reporter but otoole says there were signs that were missed and that its striking how many other people might have raised an alarm. It turns out the boss at the pizzeria where dylan worked had seen the two boys experimenting with a pipe bomb. And perhaps most shocking of all the police knew eric had a website. Ten pages of savage threats. Some frightened parents had alerted them. Police started to draw up a search warrant. But thinking they dont have enough do nothing. Sue klebold says for months and months her mind was looking for any way to deny the truth. I believed this was a moment of madness. I believed this was some impulsive fluke that happened suddenly. Reporter it wasnt until six months after columbine her denial is shattered. The lead investigator in the case who brings them facetoface with the inescapable truth of the evidence. Dylan took part in months of planning. And there he was on videotape recorded as a kind of countdown to the attack. It was horrible to see those tapes. They were posturing. They were acting tough. They were talking about all the horrible things they were planning to do. Reporter but as we said, she lives in the hell of that contradiction. She has said, i saw the end product of my lifes work. I had created a monster. But still, inside her, a mothers love for a son she lost. She hears the final word on the tape. He says, hey, mom, i got to go. Just want to apologize for any crap this may bring. Just know im going to a better place. Goodbye. He said mom. Just the fact that he said it meant a lot to me. Yeah. Reporter the tapes never released. Were told theyve now been destroyed. Since columbine, Law Enforcement says there have been 50 rampage school shootings. Abc news has estimated at least 79 thwarted plots. More than half of them mentioning columbine. So what can we do about the shooting at schools . Prevention can work but how . In dozens of cases it is fellow students who overheard something, tipped off authorities. Most of the time it is nothing. But maybe its just that one peek into what could be the next columbine. Reporter last week we tried to call every single family. Some of them expressed anger. Others said they preferred to move on. Some said they wanted to offer sue klebold their prayers and grace. So many people, as someone said, sentenced to a life of grief with no parole. After our interview is over, she walks outside in the foothills of the Rocky Mountains and tells us sometimes she finds herself drawn to a place that has a plaque with these words. It brought a nation to its knees. What have we learned . Its the columbine memorial. I feel a kind of unwelcome there. Like, of course. That perhaps im intruding. Reporter but someday if you go to that memorial, you just might see a grayhaired woman sitting there quietly alone. Sometimes i just sit there. And think. And i tell them im sorry. Reporter for nightline, im diane sawyer. Our thanks to diane sawyer. Sue klebold has written a memoir called a mothers reckoning living in the aftermath of tragedy. All the books profitsless toward research and charitable foundations focusing on Mental Health issues. Well be right back. Shopping for an suv . Well, this is the time. And your ford dealer is the place, to get 0 financing for 60 months on a ford suv. Thats right. Just announced. Ford explorer. Edge. Escape. 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To learn more about all the issues raised tonight and for resources about Mental Health and suicide prevention, you can head to our website at abcnews. Com. Thank you for watching. Tune into Good Morning America tomorrow. And as always, were online when i have an asthma attack. I feel like a fish with no water. Learn how to prevent your childs next asthma attack. Because even one attack is one too many