>> one mother's quest, looking for the path of her son's descsct and the clues she says she missed. >> the one thing of course that i want to say is, i am so sorry for what m son did. >> tonight, an important conversation about the warning signs that may prevent tragedy. >> this special edition of

reckoning, will be right back. (vo) making the most out of every mile. that's why i got a subaru imeza. love. it's what makes a subaru,

this is a specialdition of "nightline," a mother's 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. anan espspially for the families of the victims, those urgt and anguished questions never answered, until now. constitute massacre have been prevented, and warning signs that may have been missed. here's abc's diane sawyer. >> reporter: it is 1999. a shock wavav 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.

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 wasn't 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 gray-haired 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,

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 i'm sorry is such aninadequate response to all this suffering. there is never a day that goes by where i don't think of the people that 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 that about a certain need to deny what happened? >> i don know. perhaps. perhaps.

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 thissort of a mane of golden hair. it was just thick and round and -- he was suchh 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 left-hand side, i would have been one of those parents. and i guess that's why certainly why i'm here talalng to you today. >> reporter: she has written a book called "a mother's 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 hate-crazed gunman. she remembers the shocking prayer she found herself praying after learning her son might be

and the shooting was still going on. >> the policeere 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. don't let him hurt anybody. >> reporter: but by the end of the day, her son and his friend would take the liveses of 13 people and then take their own. in her boo sue klebold writes, her son wasn't the pinwheel-eyed portrait of evil we know from cartoons. he was shy, like bible, hands-on 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.

>> he wouldn'n' 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 time. >> reporter: she says h@ was easily embarrassed, tearful and hard on himself if he mad 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 interesttn 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 write 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 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 to bed. >> and you'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.

15-year-old son has bun 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 i not an explanation for a pathway to violen. dr. gregory fritz wants to warn parents tonighth 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?

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 selfonscious 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 schoooo computer system with some friends. they're 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: dylan's 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.

commandment commandments, it's wrong to steal, in no circumstances this is right. and then we responded as most parents would. we took away privileges. >> reporter: one night she's frustrated, he's not doing chores, he's withdrawn, she pushes him against the refrigerator. >> i said, you've got to stop thinking of yourself, you've got to stop being so selfish. but -- excuse me. but i gave him the old mom lecture. and then i said, by the way, today's m mhers day and you forgot it. and i don't remember how that confrontation ended. i just remember 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 being nice to say, back off, please. >> reporter: she says she blamed

>> then he w wt 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 theyeveal 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. there's something in the air. but here's the thing: about half of men over 40 have some degree o o erectile dysfunction. well, viagra helps guys with ed get and keep an ection. ask your doctoif your heart is healthy enough for sex. do not take viagra if you take nitrates for chest pain ordempas for pulmonary hypertension

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"nightline" continues. picture. can 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 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 dyn klebold. >> i don't think he was always a violent young man. i think it evolved over time. i think it took a lot of @ime. >> reporter: we 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 klebold. >> you don't think school shooters jt snap one day? >> absolutely not.t. i have not ever seen where that has happened. i think he was in a very destructive friendship which was very powerful. ybe even more powerful than

>> 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 venomou threats, graphic fantasies about revenge on people who have insulted him. people engulfed in flames, detap dated heads. according to o'toole 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 toraw weapons, swastikas, wrote about the nazis. dylan drew hearts. dylan wrote ababt his search for

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 tother. they liked violent movies and making little movies of their ow trying on what it's like to be tough guys. eric is 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 ] -- >> 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 respepe 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 if his very life was depending on it. and i would do it with lo.

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 sh. she trained at a range. and dylan klebold writes, he now has a choice. committing suicide or going nbk with eric. nbk, natural-born killer 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 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 preclude e m from being able to participate in the planning and to carry it out.

>> i don't think so. i don't think i do. >> reporter: but o'toole says there were signs that were missed and that it 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 don't 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 wasn't until six months after columbine her denial is shattered. the lead investigator i ithe case who brings them face-to-face with the inescapable truth of the evidence.

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 thty 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 life's work. i 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. he says, "hey, mom, i got to go." >> just want to apologize for any crap this may bring. just know i'm going to a better place. good-bye. >> he said mom. just the fact that he sasa it meant a lot to me. yeah. >> reporter: the tapes never released.

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 lumbine. 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 it's just tt one peek into what could be the next columbine. >> reporter: last week we tried to call every singl 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

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? it's the columbine memorial. >> i feel a kind of unwelcome there. like, of course. that perhaps i'm intruding. >> reporter: but someday if you go to that memorial, you just might see a gray-haired woman sitting there quietly alone. >> sometimes i just sit there. and thk. and i tell them i'm sorry. >> reporter: for "nightline," i'm diane sawyer.

sue k$ebold has written a memoir called "a mother'spreckoning: living in the aftermath of tragedy." all the ok's profitsless toward research and charitable foundatis focusing on mental health issues. we'll be right back. shopping for an suv? well, this is the time. and your ford dealer is the place, to g 0% financing for 60 months on a ford suv. that's right. just announced. ford explorer...edge...escape... and expedition... are available with 0% financing for 60 months. ford suvs. designed to help you be unstoppable. no wonder ford is america's best selling brand. but hurry, 0% financing for 60 months on ford suvs is a limited time offer. see your ford dealer today. whatcha dodo? just prepping for my boss' party in a aouple weeks. what are those? crest whitestrips. they whiten way better than paste. crest 3d white whitestrips... whiten 25 times better than the leading whitening toothpaste. i'd say... ...someone's making quite an impression. crest 3d white whitestrips.

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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 webte at abcnews.com. thank you for watching.

and as always, we're online tapped churches have been

in two hours, everything has changed. symbolic of that brother hood that has been ruptured for almost 2,000 years. pope francis exchanging more than just greetings, more than just gifts. really the coming together of churches at a three-hour meeting. because of the conversation he had, he can assure both churches can work together around the