this is a special edition of "nightline." a mother's reckoning. >> tonight, the massacre at columbine high school. a tragedy that shocked a left the nation asking what drove two teenagers to take the lives of 13? what kind of people were their parents? >> could you haveed at columbine? >> after 17 years, sue klebold, mother of one of the shooters, break her silence. and the families that lost so hat is it you want to say to them? >> one mother's quest, looking for the path of her son's descent and the clues she says she missed. >> the one thing of course is, i am so sorry for what my son did. >> tonight, an important

signs that may prevent tragedy. edition of "nightline," a mother's

pecial edition of "nightline," a mother's reckoning. >> good evening and thank you for join us. tonight the powerful and untold of one of the columbine shooters.

klebold is speaking out. the mother trapped inen 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 andever answered, until now. constitute massacre have been prevented, and warning signs that may have been missed. here's abc's reporter: it is 1999. a shock wave hits america. two high school boys in trench coats carrying shotguns, a 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.the terror. 13 are kill the. 24 are wounded. and we are all watching fore children run out of their school fleeing mayhem. >> a lot of students -- >> coverage of the columbine -- >> reporter: we see a wounded

escape with his life. and for the years to come, we would all be asking the same questions -- who were these d what kind of parents could produce children like these? >> someone wasn't doing their job. >> reporter: for 17 years ts of dylan klebold and eric harris have lived their secrets, unwilling to step forward. until a gray-haired woman makes her way into ahe 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. hated, threatened, she says afraid and ashame the. so klebold is now 66 years old.the families of 13 people who died and 24 people who were

what is it 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 such an inadequate response to all this suffering. there is never a day that goes by where i don't think oft dylan harmed. >> you use the word harmed. >> i think it's easier for me to say harmed than killed. it's still hard for me after all this time. >> is thateed to deny what happened? >> i don't know. perhaps. perhaps. 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 . he had this sort of a mane of golden hair.

and -- he was such a happy,, brilliant little child. >> for all the parent hot have said, i would have something, i would have just known. >> i know. before col would have been one of those parents. and i guess that's why certainly why i'm here talking to you today. >> reporter: she has written a book called "a mother's 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 the mother of a hate-crazed gunman. she remembers the shocking prayer she found herself praying after learning her son might be one of the c 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--

and then at that moment i prayed that he would die.. just make it stop. don't let him hurt anybody. >> reporter: but by the end of the day, her son anduld take the lives of 13 people and then take their own. in her book sue klebold writes, cartoons. he was shy, like bible, hands-on parents, put them to bed with and hugs. >> reporter: sue klebold calls dylan her shiny penny. in gifted classes. loved little league. gave big hugs and kisses.ut of legos. >> he wouldn't just work on one puzzle, he'd dump them into a big mountain so he could solve five or six of them at the same r: she says he was easily embarrassed, tearful and hard on himself if he made a mistake.

>> he talked about looking s 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 she is male a big mistake. her son is changing. but she writes off the changes. as an adolescent phase. >> sometimes he would or quiet. and i remember asking him, are you okay? are you sure you're okay? you seem so tired. and he'd stand up and say, i've got a lot of homework, i need to go toou'd let it go. >> i let it go. and that's the difference. i would dig. if it were me today, i would dig and dig and dig. >> reporter: she has no idea her son has begun a secret journal. and his first entry is this. i hate my life, i want to die. i have a nice family, good

no girls. nobody accepting me even be accepted. but at this point we want to be very clear -- 80% to 90% of depression can be treated. and even is not an explanation for a pathway to violence. dr. gregory fritz wants to warn parents tonight that suicidal depression is real and can teen anywhere. >> somewhere between 15% and 20% of high school kids say that they have thought about suicide in the past year. than 17 years ago, sue klebold says she knew so little about teen depression. >> could you have prevented what happened at columbine? >> ifd that dylan was experiencing some real mental distress, he would not have been there. he would have gotten in this video from his junior year he seems self-conscious but talks about

>> so you get better chancesl 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 all suspended for three days. he scratches an epithet on the locker of a kid he thinks is taunting him. then the big shock, heak into a van, steal electronic equipment, and police make an arrest. >> this is a felony, two felony s terrible, i know, absolutely. it was awful. and at the time i thought that was the worst thing i could ever possibly experience. >> reporter: dylan's cold reaction after the arrest scared and shocked her. he acted as nothing wrong. she says she gave him one of her lectures, trying to reason with him. >> i even talked about the ten commandment s wrong to steal, in no circumstances this is right. and then we responded as most parents would. we took away eporter: one night she's

chores, he's withdrawn, she pushes him against the refrigerator. >> i said, you've got to stop thinking of yourself,top being so selfish. but -- excuse me. but i gave him the old mom lecture. and then i said, by the way, mothers day and you forgot it. and i don't remember how that confrontation ended. he softly said, mom, please don't push me, i don't know how much i can control myself. it wasn't a scary thing. it was just him 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 --e water king with african violets in it. and i thought everything was fine.

sweet.e come back, the secret journals. what do they reveal about the minds of two teenagers responsible for columbine? and what forced sue finally face the truth about her son? tonight, what experts tell us might prevent a tragedy. the setting is just righin the air. but here's 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. doctor if your heart is healthy enough for sex. do not take viagra if you take nitrates for chest pain hypertension your blood pressure could drop to an unsafe level. to avoid long-term injury, seek immediate medical help for an erection lasting more than four hours.agra and call your doctor right away if you experience a sudden decrease or loss in vision or hearing. ask your doctor...

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lease a 2016 lincoln mkx for $399 a monthur lincoln dealer. this special edition of "nightline" continues. >> look at a kind of classn you pick out which ones will grow up to be school shooters? almost two-thirds will be from two-parent homes. nearly half of the kids will do

arrested before. and yet every child you see here will become a school shooter. in total murdering 67 people. in this picture is dylan klebold. >> i don't think he was always a violent young man. i think it evolved over time. i think it took a lot ofe brought in former fbi agent mary ellen o'toole, one of the world's leading profilers of the criminal brain. she has analyzed thousands of pages of evidence on columbine and dylan you don't think school shooters just snap one day? >> absolutely not. i have not ever seen where that has happened. very powerful. maybe even more powerful than what we think. >> reporter: there is no way to continue telling this back to another picture. a friend who was with him breaking into the van. eric harris.

shooter at columbine that day. begun to keep a secret journal, and his journal is filled with venomous threats,t revenge on people who have insulted him. people engulfed in flames, detap dated heads. according to o'toole itsonality disorder, a psychopathic brain. >> these are people without a conscience. these are became without empathy, without guilt. >> reporter: different from dylan klebold? another expert on columbine, dr. peter lang man, insists he is. >> eric liked to draw weapons,s, wrote about the nazis. dylan drew hearts. dylan wrote about his search for true love. eric when he does refer to girls, his fantasy isthem. >> 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.

tough guys.smooth. >> i think we might have to get some more weaponry. >> reporter: dylan stumbles. >> it's a good thing we uh -- we ordered those radio [ bleep ] -- 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.ne 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 shepect his privacy with distance and regret she now says how wrong that decision was. >> would you ransack his room now? >> i would. i'd do it as 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, enough to buy them legally, got them three at a gun show.

and dylan klebold writes, he choice. committing suicide or going nbk with eric. nbk, natural-born killers, the violent revenge movie by oliver stone.gs us to the central question about dylan klebold. why did he go from suicidal to homicidal? did eric infect him with a kind of patholo or was it dylan's presence that reinforced eric's violent fantasies? >> do you think dylan klebold knew right from wrong? >> yes, absolutely he did. but it did not being able to participate in the planning and to carry it out. >> do you believe in evil? >> i don't think so.t think i do. >> reporter: but o'toole says there were signs that were missed and that it's striking how many other people might have raised an alarm. it turns out the boss at the dylan worked had

with a pipe bomb. and perhaps most shocking of all the police knew eric had a website. ten pages of savage frightened parents had alerted them. police started to draw up a search warrant. but thinking they don't have enough do nothing.ys for months and months her mind was looking for any way to deny the truth. >> i believed this was a moment of madness.was some impulsive fluke that happened suddenly. >> reporter: it wasn't until six months after columbine her denial is shattered. the lead investigator in the case who brings themith the inescapable truth of the evidence. dylan took part in months of planning. and there he was on videotape kind of countdown to the attack. tapes. they were posturing. they were acting tough. they were talking about all the

>> reporter: but as we said, she lives in the hell of that contradiction. she has said, i saw the end product of myi had created a monster. but still, inside her, a mother's love for a son she lost. she hears the final word on the tape."hey, mom, i got to go." >> just want to apologize for any crap this may bring. just know i'm going to agood-bye. >> he said mom. just the fact that he said it meant a lot to me. yeah. >> reporter: the tapes never released. we're told they've now been destroyed. since columbine, law enforcement says there have been 50 rampage school shootings. abc news hast 79 thwarted plots. more than half of them mentioning columbine.

shooting at schools? prevention can work but how? in dozens of cases it is feludents who overheard something, tipped off authorities. >> most of the time it is nothing. but maybe it's just that could be the next columbine. >> reporter: last week we tried to call every single family. some of them expressed anger. preferred to move on. some said they wanted to offer sue klebold their prayers and grace. so many people, as someone said, life of grief with no parole. after our interview is over, sheoothills 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 what have we learned?

>> i feel a kind of unwelcome there. like, that perhaps i'm intruding. >> reporter: but someday if you go to that memorial, you just might see a gray-haired woman there quietly alone. >> sometimes i just sit there. and think.m sorry. "nightline," i'm diane sawyer. >> our thanks to diane sawyer. sue klebold has written a memoir called ckoning: living in the aftermath of tragedy." all the book's profitsless toward research and charitable foundations focusing on

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to learn more about all the issues raised tonight and fortal health and suicide prevention, you can head to our website at abcnews.com. thank you for watching.

from new york, almost live, "comics unleashed" with your host, byron allen. and >> well. yeah! thank you. that is great.