>> announcer: this is "nightline." >> tonight, the tape versus the testimony. that chilling dash cam video played out in court today. the chicago police officer charged with the murder of a black teenager, shooting him 16 times. >> he waved the knife from his lower right side upwards, across his body, towards my left shoulder. >> now taking the stand in his own defense. >> i'm yelling at him, drop that knife. >> and he never dropped it, right? >> he never dropped it. >> his decision to testify, a risky move or an opportunity to prove that his actions were justified. plus, beneath the beauty for 15 years, she was the highest paid super model on earth. today, giselle bundchen sharing

her deeply private struggle. >> living like this was very hard. i was trapped and i couldn't breathe. >> the panic attacks that led to that pivotal moment. robin roberts and the exclusive interview. first, here are the "nightline" five. at ikea, we believe that everything you need should be within reach. that anything that matches your taste can match your budget. that green living doesn't have to cost much green. we believe that you should always have room for the little things.

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good evening, and we start here with the chicago police officer giving emotional testimony today in his own defense. officer jason van dyke is on trial for murder after he shot a young man named laquan mcdonald 16 times, all of it caught on camera. it's a case that has provoked outrage across the country and abc's alex perez is on the story. >> reporter: it's these tense moments from 2014 now under scrutiny, chilling dash cam video showing a chicago police officer shooting 17-year-old laquan mcdonald 16 times, killing him. today, that officer, jason van dyke, taking the stand in his own defense. >> his face was just expressionless, turned his torso toward me. >> reporter: charged with first-degree murder, van dyke testifying he feared for his life and fired only after mcdonald ignored repeated commands to drop a three-inch knife during the incident. >> i was yelling at him, drop

the knife. i yelled it i don't know how many times but that's all i yelled. >> reporter: in the four years since the shooting, this case has become a flash point in the ongoing tensions between police and the black community in america. prompting nationwide protests. >> we just want justice. we're out here marching and protesting to make sure it doesn't happen again. >> reporter: it was october 20, 2014, when van dyke responded to a call about someone with a knife trying to break into vehicles. mcdonald was holding a small knife in his right hand. police dash cam video shows van dyke getting out of his squad car and opening fire within six seconds. autopsy reports would show mcdonald had the drug pcp in his system the night he was killed. from the beginning, van dyke has maintained he acted in self-defense. chicago mayor rahm emanuel and

city attorneys fought to keep the video from becoming public, but just over a year later, a judge ordered the video be released. van dyke was charged with first-degree murder the same day. >> it is graphic. it is violent. it is chilling. >> reporter: van dyke's defense argues he feared for his life when he opened fire. >> this is not a murder case. despite what you heard in the courtroom. >> i would definitely call it excessive force based on the dash cam video. mr. mcdonald is walking away from the officer and posed no immediate threat. best practices for using deadly force is as a last resort. >> reporter: the video of mcdonald's death sparked months-long protests in chicago and across the country. >> 16 shots. >> the sooner you can release information, the better for the community, and because there was such a delay, for whatever reason, the delay really just builds more distrust of law om tensions high, chicago's top

brass was on edge. >> jason van dyke will be judged in a court of law. that's exactly how it should be. >> reporter: at the time, abc news confirmed 18 complaints filed by citizens against van dyke since he joined the force in 2001, including allegations of using excessive force and racial slurs. but van dyke was not disciplined. >> if we don't get it, shut it down. >> reporter: under public pressure, emanuel fired then chicago police superintendent gary mccarthy. >> now's a time for fresh eyes and new leadership. >> will everybody please be seated. >> reporter: finally, last month, the long anticipated trial. >> defense call your next witness, please. >> reporter: today, an emotional jason van dyke explaining what happened in his own words. >> he waved the knife from his lower right side upwards, across his body, towards my left shoulder. >> and when he did that, what did you do, officer? >> i shot him.

>> reporter: what jasonan dy's tes iselto thanideo and needed to get across. >> reporter: defense attorney saying this was self-defense, using a measuring tape to mark the 13 feet between the two men. an expert in police use of force showing how quickly mcdonald could have come at van dyke with the knife. >> and i'll show you how much time you would have to react to me. >> reporter: the defense also submitting an animation aimed to depict the officer's perspective and counter the police dash cam video. ultimately, jason van dyke's defense is that he was justified when he pulled the trigger because he believed that laquan mcdonald was moving the knife from his waist across his chest and up over his left shoulder. that's what jason van dyke testified, and jason van dyke believed that was enough of a threat to return force with force. >> reporter: but prosecutors wondered why if van dyke felt threatened he's seen walking

towards mcdonald. >> you had six seconds before you pulled the trigger the first time. right? >> and in that sex secondix sec got a lot closer to me than i could have gotten away. >> and you got a lot closer to him too, didn't you? >> i know that now, yeah. not intentionally. i thought i was back pedaling that night. >> you thought you were back pedaling as you're firing shot after shot after shot? >> what i know now and what i thought at that time are two different things. >> reporter: prosecutors relying heavily on the video, playing it dozens of times throughout the trial. >> can you see that? >> reporter: arguing the officer's use of deadly force was unjustified. >> did you ever make a decision to stop shooting that night? >> yes, i did. >> and when was that? >> once i recognized that he hit the ground. >> well, he hit the ground and you continued to shoot, correct? >> reporter: and pressing on why

he kept shooting after mcdonald collapsed, van dyke at first saying he thought mcdonald was trying to get up. >> was there any point in that video where laquan mcdonald was trying to get up? >> in that video, it may not show it but that wasn't from my perspective, ma'am. i was coming at a completely different angle. >> reporter: he also says he continued to fire, aiming at the knife. >> so why would you continue to shoot at his knife? that's not what you're trained to do. >> my focus was just on that knife and i just wanted him to get rid of that knife. that's all i could think. >> i think the most striking thing about this incident is the number of shots. we're trained, as cops, to fire several volleys and assess. it ended up being 16 shots. that's beyond the pale of what's needed to stop a suspect. >> reporter: jurors in this case are probably going to focus not on the number of shots fired, not on the number of seconds that ticked by between this

defendant's "arrival" and when he pulled the trigger but rather jurors are probably going to look at what the victim was doing in the split seconds before officer van dyke pulled the trigger, and then, if jurors believe that the officer was justified in perceiving that threat as a serious threat, then this officer walks. >> reporter: it's that question that makes these types of cases notoriously difficult to prosecute. each instance unique, but the common thread? an officer who felt their life was in danger. a grand jury decided not to indict timothy allowman, who shot and killed tamir rice. betty shelby was found not guilty and not guilty in the death of philando castille. if convicted, van dyke could face life in prison.

the case could go to the jury as early as next week. i'm alex perez in chicago. next here, beneath the beauty, robin roberts and the exclusive sitdown with super model giselle bundchen, the darkness she felt in the spotlight. my name is elaine barber, and i'm a five-year cancer survivor. surviving for five years is a big deal. i had so many people at ctca helping me find a way to go through the treatments. the reality of cancer is not everybody survives. at ctca, they have a huge celebrate life event. that was amazing, because the whole day was about all of the survivors. i'm excited about my future. visit cancercenter.com to schedule an appointment now. endless shrimp is back at with all the shrimp you want, any way you want them. there's new sesame-ginger grilled shrimp with savory soy-ginger sauce and sprinkled with asian seasoning.

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she is one of the most recognizable super models on earth, but it took some time for giselle bundchen to recognize some difficult parts about

herself. bundchen struggled with anxiety, even panic attacks, and her new book details how she course corrected on a path to what she says is now a meaningful life. she sat down with our robin roberts. >> reporter: giselle bundchen is a force to be reckoned with, one half of the world's most famous power couple. and the epitome of glamour. she has been one of the world's top super models for 20 years, appearing on the covers of over 1,200 magazines. and starring in ads for luxurious companies like dolce & gabbana, but the giselle we know, says she didn't always exist. we joined her at her home in boston where she discussed her candid new book, which is out today. you never really thought about being a model but it was a wonderful opportunity and you took every opportunity. >> i was 14 years old, so while

thinking i was very grown up, i was like, i'm going to move out and make a living. i'm already 14. i'm so old. i was 5'10" at 14 and i was so awkward. >> reporter: you were one of those that would slump. >> everyone was making fun of me. it was a surprise to me when someone looked at me in the mall and was like, hey, do you want a to be a model. i felt really early that if i was me, you know, and this was the model, then it was very easy for me because i could go there and be very objective. it was very simple. it was a character i was playing. >> reporter: as a top model in high demand, working 350 days a year, giselle found herself bowing to the enormous pressure. it is so hard to believe where you are now that in your 20s, there was a time that you had panic attacks. >> it started all in a little plane. i was in costa rica in a six seater plane and the plane started shaking like a little leaf. i mean, i was like completely --

this sense of powerless and i'm a person who always likes to have things under control. that was definitely out of control moment, and it kind of started this kind of fear of being in small spaces. so, it started with a little plane ride but then it became like tunnels, subways, elevators, i mean, i lived on the ninth floor of an apartment and i wouldn't go up nine floors of stairs because i was scared that i would, like, suffocate. i mean, it was crazy. my world just kept getting smaller and smaller. i was in a hamster wheel going 500 miles an hour, you know, as a model, i saw so many girls come and go so i'm just going say yes to everything and live the life in such a fast paced really, like, running myself to that point of creating that anxiety attack. >> reporter: her crippling anxiety attacks would lead to one of the most challenging moments in her life, the moment she considered jumping off the ninth floor of her new york city

apartment building. and you said at one point, where you were in that apartment on the ninth floor, that you went out on the balcony and what was going through your mind? >> well, because -- sorry. sorry. god. that moment, when i was standing there and i had this thought like, living like this was very hard because life was so -- it was like i was trapped and i couldn't breathe and even outside of my own balcony. so, i feel that i wanted to share that, to show others that there is a light at the end of the tunnel, and from that moment on, you know, i realized that my life needed to change. >> reporter: that change came when she began prioritizing her health and what she put into her body, taking up yoga and meditation. >> and when meditation came into my life, you know, everything

became clear, because i was going such a fast pace and everything stopped. i was able to notice and see a lot of different things that i never was aware of. first, that my body was my temple and what was i putting in my body and what was i doing to myself. >> reporter: because you were drinking coffee, a pack of cigarettes. >> every day because it was the only time i was breathing, actually, because you know, it was the only time i would actually breathe. >> reporter: her marriage to new england patriots quarterback tom brady was a turning point. >> i've always wanted to be a mom. i've always wanted to have a family. and that was, you know, when i became a mother, it really became my priority. >> reporter: it was a different pace than her former jet setting model life, but one she fully embraced. >> i just wanted to be with my kids. when i thought about something, i thought about my kids. it was like, i want to be with them. >> reporter: becoming a mother to benny and vivian and stepmother to tom's son, jack, changed her life in unexpected ways. she took a deliberate step back from modeling to focus on her

family and support her husband's nfl career. >> i just wanted so much to be there for my children and to be there for my husband too. you know, because for him to have the space to live what he loves so much and i was actually living what i love so much which is being a mom and a nurturer and taking care of my family. >> reporter: she often shares personal moments of the happy family on instagram with tom's calming presence a key part of their relationship. >> so, he has that kind of cool and collected thing about him. he's just very, like, you know, grounded, and i feel like, you know, i'm very emotional and very changeable and, you know, like just me. but what i've learned from him is to kind of take a breath. >> reporter: the super star couple's life together has often been the subject of intense scrutiny. with near constant speculation over tom's eventual retirement from football. you also put to rest in the book

because, you know, tom has talked about his retirement. it's a big subject, especially here in the boston area. and he kind of said, i'll play five more years and you have said some other things but in the book, you kind of said what will be will be. >> yes, because when you love someone, you want them to be happy. >> reporter: at 4 1, brady is showing no signs of stopping. as seen in his most recent game against the miami dolphins. part of tom's enduring success, the couple's healthy lifestyle. one filled with plant based foods. what is this fascination that the public has with you and tom, your eating habits? >> i don't know. >> reporter: what is that about? >> i don't know. i love food. and i think, you know, i reallye your medicine. >> reporter: it's a belief that she takes seriously, picking vegetables and fruits with her children from her own garden. by revealing her own struggles, she hopes that she can share life lessons she'd learned along the way, including the most important one of all. >> what we all are is light and

what we all are is love, and if you remember that, the size of our stories, if you can connect to that, then if you take anything from the book, it's just live your life with love. >> reporter: for "nightline," i'm robin roberts in boston. and we should say all proceeds from bundchen's book will go to a brazil-based nonprofit committed to improving water sustainability. coming up next here on "nightline," the first lady emming her first solo trip and getting hugs in return. bracing and getting hugs in return. >> announcer: abc news "nightline" sponsored by geico. when i was shopping fothe choice was easy. i switched to geico and saved hundreds. excuse me... winner! that's a win. but it's not the only reason i switched. hi! geico has licensed agents who i can reach 24/7.

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and finally here, their ie withump t momen embraced the children in a hospital in ghana, watching the staffuttional program highlighting her be best initiative which focuses on the

well being of children. and we'll have much more on the first lady's overseas trip in the coming days. meanwhile, we want to thank you for watching "nightline" tonight, and as always, we're online 24/7 on our "nightline" facebook page. thanks again for watching, and good night.