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tonight on "20/20" -- in an instant. gunshots. shen a human stampede. this week in denver. when life changes in a split second and the crowd goes wild, what can keep you alive? >> everybody wants to get close. this is getting dangerous. >> who runs? who helps? and who becomes paralyzed with fear? >> i basically just froze. >> crowd control. crazed employees coming back for revenge. >> he looked like he was possessed. >> how quick thinking can outwit a gunman on the loose in your office. with nothing but office supplies and the clothes off your back. >> it's the fire drill, right? we should be doing gunman drills? >> action plan.

even highway pileups. 118 cars. slamming together in the fog. >> oh, my god. oh, my god. just tons of trucks and cars. >> how to survive this one, by not doing the obvious. collision course. plus, a knock on your window. then, carjacked. the boston carjack victim, taken for a midnight ride of terror. >> you have no no idea what's going to happen. >> exactly. other than you think you're probably going to die. >> how he saved himself and maybe hundreds more. tonight, do you follow, do you fight or do you flee? when life changes in an instant. here now, david muir and elizabeth vargas. >> good evening. new york city could have been next. that is what investigators are now saying was the next target for bombing suspect dzhokhar tsarnaev, who tonight is in fair condition after being

transferred from a boston hospital to a medical facility in a state prison. >> of course, so many asking tonight, elizabeth, what if those brothers made it to new york to times square. the crowd chaos could have been boston all over again. so, what decision do you make in indiana stand, when it can make the differences between life and death? here's matt gutman. >> reporter: there is a moment when, in a crowd, split-second decisions have to be made. it happened dozens of times in boston last week. >> people kind of freeze and a we just started to react. >> wait, where is everyone? there's got to be people hurt up there! >> that instant is really amazing, some of us are hardwired to run. and other people are hardwired to fight. i need to go help, people are in distress and i go. and then there's people that go, "oh my god, it's too much for me. i need to leave."

>> reporter: in an instant humans can cease being individuals, turning instead into a herd, blindly moving in a single direction. a swarm of screaming tweens tear through the gates just to catch a glimpse of the jonas brothers. a river of soccer fans streaming through the stadium gates at the world cup. and amidst the solemnity of a presidential funeral. everybody wants to get close to the body of the man they so revere and so idolized but this is getting dangerous. just this week in denver, 20,000 people gathered for a marijuana rally. but soon, the pot smoke turned to gun smoke when shots rang out. instantly, mellow turns to mayhem. >> there were just so many people literally just running at people.

nning.f people just massively >> reporter: the crowd bolting, pushing, shoving and trampling to escape. it wasn't bullets but bargains that caused this swarm to charge towards a black friday doorbuster deal. >> in the shopping stampede, this man was trampled to death. . >> carl jung said, you put 100 clever people into a group, they lose their intelligence. >> reporter: it is at those times that we become frighteningly similar to a herd of cattle. >> what's fascinating about crowds is that we all tend to follow them. we don't tend to stand up and be individuals in them. we tend to want to blend in and be part of it. >> reporter: just look at the classic psychological experiment illustrated here. this woman sits quietly doing her work. then smoke starts pouring in.

she's visibly worried. still, five minutes go by. the other people in the room, all in on the experiment, ignore the smoke. >> she's just sitting there. no one else is reacting. >> reporter: 10, 15, 20 more minutes pass. still, she doesn't take any action, because the others don't. in comparison, a second subject, in the room alone, reacts immediately and leaves. >> that's how powerfully socialized we are. >> reporter: socialized to death in some cases. >> and that's what that experiment shows. >> reporter: in january, nearly 2,000 people packed a nightclub in brazil, doubling its capacity. the band sparks up fireworks. within seconds, fire engulfs the club. people try to flee. unquestionably following the crowd to a single exit. a stampede. people start falling. stacking up like cordwood. blocking the entrance. more than 200 died. those are the doors through which nearly 2,000 college students tried to squeeze through.

as that fire raged, you can also see here, where good samaritans and firefighters used sledgehammers to break through into the bathroom and try to drag people out here to safety. there are those few, who in an instant, decide to run against the grain, surging towards the flash point. >> a life experience can force you to think about things differently and then do things differently. >> reporter: carlos "the cowboy" arredondo, whose son was killed in iraq, was a spectator at the marathon. we first noticed him, amidst the carnage at the finish line, because of that hat. but what made carlos stand out was when most people sprinted away, he stayed. >> i just jumped the fence and i ran towards the other side to see if i can help in any way i can. >> reporter: psychologists tell us what distinguishes ordinary man from hero is a unique ability to ignore basic instinct.

>> when i stepped into the street, you get a sense of tunnel vision. and i ran as fast as i could to the epicenter of the blast. >> reporter: michael chase was a few away from the second boston explosion. yet, he ran in to help this young child. >> i didn't think twice about it i was looking just to help people. >> reporter: for others, their call to action is in the palm of their hand. images taken at the scene, often capturing the precise moment of impact. when the stage collapsed at a sugarland concert in indiana, david wood was barely an arms length away. he managed to shoot this video with his cell phone. >> it was chaos. are you okay? i threw my arms in my wife's back and shoved her. i knew she was safe. it was just kind of instinct to crawl back in and help the ones that were screaming that were in need.

we need a medic really bad. it's a little girl! >> reporter: while some may criticize those who whip out their camera during tragedy, others say it could be a new tool. people don't necessarily have to risk getting hurt to be able to help. >> if i have a camera here and i am taking pictures, i am not jumping in as much. i'm more protected. and that's safer to a lot of people. it's a more passive way of being part of the action. >> reporter: just last week, cell phone snaps like these helped authorities in boston identify the alleged bombers. but for mike, gumjumping in is only option. >> i'd do it all over again. that's not something you think about before hand. it just something that you do. next -- hundreds of pieces of crashing metal. one of the worst pileups in u.s. history. 118 vehicles.

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"20/20's" in an instant continues. here now, john quinones. >> reporter: thanksgiving morning 2012. interstate 10, west of beaumont, texas. the highway crowded with holiday travelers. >> happy thanksgiving, everyone. we're looking at fog in the morning. >> reporter: on one of the busiest travel days of the year, fog and speed, the limit recently raised to 75, form a perfect storm for a highway catastrophe. you will never forget this thanksgiving. >> no, no, no. not anytime soon. >> reporter: catie and matt stegmoyer heading for ohio with their children. they drive from sunshine into a wall of fog. >> i mean, fog like i had never seen it. it was so thick that it was actually, i had to use the wiper

blades, because it was condensing on the windshield. >> reporter: police dashcam video of i-10 that very morning. in an instant, daylight to danger. through the fog, catie stegmoyer spots a truck dead ahead. she stops just in time, but all around, other drivers fly blissfully right on by. >> i kept telling matt, they don't know, they don't know, they don't know to stop and then they started piling up on each other. >> reporter: ahead, a mazda has rear-ended a chevy tahoe. it's a simple fender bender. but it sets off one of the biggest chain reaction crashes in history. >> a massive crash. >> mangled metal as far as the eye can see. >> bam, you could hear it for miles. >> reporter: somebody described it as a demolition derby. >> i think that would probably be a fair assessment at that point in time, yes. >> reporter: a sense of the bedlam in texas from other

crashes caught on camera in another place and time. imagine that, multiplied by 100. back in texas on thanksgiving morning, the full-contact traffic jam continues. >> there's a major accident! on i-10, i mean, there's tons of trucks and cars. >> big rigs hitting big rigs and hitting little cars. >> oh, my god, oh, my god. >> reporter: police and cell phone video reveal an instant junk yard. but only from the air does the scope of the destruction become clear. more than a mile of mayhem. 24 separate crashes involving 118 vehicles. >> look at this. kids on the side of the road. oh, my god. >> reporter: stunned travelers emerge from cars. they wander through still dense fog in the highway median. in this part of texas, everything depends on local first responders.

the nearest is the hamshire volunteer fire department. nick morrison, an oil field worker becomes incident commander. >> cars are still coming. and the fog isn't lifting. and, just how much bigger is this going to get? >> reporter: when is it going to stop? >> you couldn't see, so you didn't know where the cars were going, where they were wrecking, or if they were going to come and hit you. >> reporter: down the highway, the stegmoyers are still in the eye of the storm, they just don't know it. catie, a nurse, wants to help. so, your nurse's instincts kicked in? >> yes. i liked to think my motherly instincts kicked in first, and i said, you guys are okay here, i'm going to check on other people. >> reporter: but the wreck isn't over. in the fog, where his wife just disappeared, matt hears another collision. >> there was a giant semi on top of a car where my wife was. >> reporter: eventually, catie calls. shaken by a close call, but unharmed. >> when i finally got ahold of him, he just held me, and he's like, i thought you were dead,

and i said, i almost was. >> reporter: but the pileup isn't finished with them. a white suv plows into a car behind theirs. matt stegmoyer knows, usually in an accident, it is safest to stay in your car. but there is nothing usual about this accident. you knew you had to get out. >> yeah, it was just, it was just a bad feeling. >> reporter: matt has a wrenching choice -- conventional wisdom says, stay in the car. but survival instinct says, go. in a flash of father's intuition, he decides. >> and so, i grabbed both kids and ran. >> reporter: and not a moment too soon. a semismashes into the pile, crunching their car, which is now, fortunately, empty. >> the back of the semiwas right where brandon's head was. and i looked at it and i just -- i said, my kids were in that car. >> reporter: but the couple in that white suv just behind the stegmoyers did not and could not run away.

when that truck hit, they were killed. the only fatalities in the entire wreck. and it happened just inches from where the stegmoyer children had been. >> you could hear cars hitting in the fog and you could see he headlights going back and forth as people were swerving. >> reporter: drive david perryman helped carry stretchers and comfort the injured. he remembers one particular young man. >> i was trying to take his mind off of what was happening. i said, what do you like about thanksgiving dinner, what is your favorite part of it? and he almost smiled and he whispered, "all of it." >> reporter: chain reaction multivehicle crashes are usually caused by snow or fog. which was the cause of this 95-vehicle crash in virginia on easter sunday. they happen more often than you may think. there were 44 deadly pileups of

ten or more vehicles between 2007 and 2011. and the stegmoyer's, well, they reached ohio where their long-delayed thanksgiving was sweet. you had a lot to be thankful for. >> oh, gosh yes. we pulled into his parents' driveway and his mom, in the driveway, she just, tears coming, i'm crying, she's like, give me my babies, you know? and it came so close. it came so close. >> and throughout tonight's program, we're on twitter. we want to know about the decisions you've made in an instant that might have saved your life. tweet us, use #abc2020. elizabeth and i will be right back. next -- when your workplace turns into a killing field. >> he's chasing me around the table, like a sick game of tag. >> the three words you need to know that could save your life. coming up. ♪

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it's not just going postal anymore. identities going crazy, with a gun, in almost any workplace. so, how can you defend yourself? i found out on a tour through our very own "20/20" offices. but a practice run is nothing compared to being in the middle of it, in real life. it was a bustling friday morning on the sidewalk in front of new york's iconic empire state building. irene timan and a colleague were walking to their office together when, in an instant, they were confronted by a deranged coworker with a gun. >> he looked like he was possessed. and it was just like a blank stare. >> reporter: the shooter was 58-year-old jeffrey johnson, an aloof and eccentric man from the design company where they worked. >> very withdrawn, very isolated.

didn't talk. >> reporter: so you were basically all walking on eggshells around him. >> yes. >> reporter: johnson was an office rival with one worker in particular, steve ercolino, a confident and outgoing salesman. >> jeff just, for some reason, did not like steve. >> reporter: after johnson was fired, the bad blood between the two erupted in a confrontation in the elevator. >> jeff threw an elbow into him and i think at the point steve grabbed him and threw him up against the wall. and jeff said, "get your hands off of me, i'm going to kill you." >> reporter: he actually said that. >> he said, "i'm going to kill you." >> reporter: months later on that fateful friday morning, irene was walking to work with ercolino when johnson came out of nowhere, pistol in hand, to make good on that promise. >> he put the gun right into steve's chest. >> reporter: so, took the gun, pointed it and tugged the trigger. >> uh-huh. >> reporter: ercolino was killed instantly. chaos erupts on the sidewalk and surveillance video shows police moving in and gunning down johnson. as for irene?

what did you do? >> nothing. i couldn't even scream. i couldn't warn him or anything. i basically just froze. >> reporter: irene's reaction was hardly unique. >> shooting four employees before -- >> reporter: experts say 80% of us freeze when confronted with disaster or danger. even though hundreds are killed every year in workplace shootings, most employees are clueless about how to react when confronted with a coworker turned killer. like these panicked workers at a kentucky plastics plant in 2008. much more rare, the cool-headed response of school supervisor bill husfelt during this wild incident. a deranged man pucks out a gun and threatens a school board meeting. >> i don't want anybody to get hurt. it was the only tool or weapon i had was my tongue. and so there was nothing else we could do but talk to him and try

to calm him down. >> please don't. please don't. please. oh. >> reporter: the gunman fires point blank at husfelt and incredibly, he misses. fortunately, an armed security guard arrives and wounds the shooter, who then kills himself. >> the game has changed. you need to react. the first five seconds of an active shooter incident is paramount. >> reporter: workplace safety consultant john bruner says in moments of crisis, our brain's deliberative function can be overwhelmed. on the other hand, our muscle memory, things that we've practiced over and over, can kick into overdrive. and that's how you can save your life. this training video produced by safety officials in texas shows what you should do. gone is the old advice to wait in place for help to arrive. now, there's a new strategy. option one? run. >> if you're in this situation, elizabeth, and you know that the shooter is pretty far away right

here, we have an exit. we're going to tell people, we have a shooter down the hall. let's exit over here. >> reporter: if there's no quick way out, use anything to create a distraction. a fire extinguisher can create a literal smoke screen. >> if you train for these situations, you will strengthen that muscle memory. >> reporter: it's sort of like the fire drill, right? we should be doing gunman drills? >> we're getting to that stage. >> reporter: but say you're trapped and there is no way to run. option two? hide. in the bathroom without a lock? bruner says improvise by using a belt to slow down entry. and if you have to hide inside an office -- >> we lock this door. if you have any secondary devices, these will be, these will assist you. >> reporter: like a doorstop? >> like a doorstop, absolutely. >> reporter: okay. but what if you're cornered in your office and the gunman finds your hiding spot? >> if you're hearing him bust through this door, you have to quit the hide and you have to attack. >> reporter: option three? fight. the minute he comes in the door i go at him? >> you need to be aggressive.

you have to fight for your life. >> reporter: look around for anything that could be used as a weapon. taking those scissors and where, what do i do? do i go for their throat? >> you go for any piece of body you can. maybe you need to stab him in the shoulder, maybe you need to stab him in the face. it becomes survival. you have to develop a survival warrior mind set. >> reporter: great advice to be sure, but what if you are literally out of options and you're looking down the barrel of a gun and defenseless? can you still survive? zach emenegger is living, walking proof that you can. in 1999, zach was a 21-year-old worker on the overnight shift at a supermarket in las vegas. in a case of random violence, a deranged gunman named zane floyd walked in through the door with a loaded shotgun and started shooting everyone in sight. >> he comes around the far corner and he points the gun at me and he takes a shot, over the produce table, it goes over my head, so, i'm staying low.

and he's basically chasing me around the table, almost like a sick game of tag. it was almost right on top of me and shot me, pretty much at point blank range. i felt the blood pour out of my body. >> reporter: but floyd wasn't finished with zach. he shoots him a second time, hitting his arm. wounded, desperate and cornered, zach is out of options. but in an instant, something clicks in his head. >> there's just something i do remember being a little kid, something just stuck in my head. if i was in a situation like that, to where there was nowhere to go, you play dead. i jerked my whole body and i played dead and he actually said, yeah, you're dead. >> reporter: and zach was smart enough to keep playing dead because after killing another worker, floyd doubles back in zach's direction. >> you see it on the video tape that he actually steps over my body and, you know, just to make sure. >> reporter: by this time, police have surrounded the supermarket and floyd

surrenders. he was convicted of murdering four people and is currently on death row. while every workplace shooting scenario is different, whatever the reaction made in the instant of a crisis, all survivors are like little to share one common sentiment. >> i'm happy to be alive. the good days and the bad days, you know? it's something i got through. i'm blessed. next -- a knock on your window, then, carjacked. >> the person who gets in the car said, remember that bombing that happened at the marathon? i did it. >> so, how did a near empty gas tank, a left behind cell phone and a split-second decision all save his life? and possibly hundreds of others? when we come back. we're in los angeles with the bing it on challenge to show google users what they've been missing on bing. let's bing it on. [fight bell: ding, ding] how many here are google users? what if i was to tell you that you would actually like bing way more than google when it came to the results? prove it.

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we know it is impossible to predict what you would do if someone snatched your car with you still in it. but you're about to find out from the man whose life changed in an instant, what he sen he s two boston bombers took him hostage.

the carjacking victim was quietly trying to figure out how to save his own life and, perhaps, hundreds more. here's dan harris tonight. >> reporter: with each passing day after the boston marathon saga, there is one event that further emerges as a truly pivotal moment. it happened here, at an otherwise unremarkable gas station. one young man's brave and desperate act may be the very instant when the tide of terror started to turn. if this fie hadn't escaped and called the cops, these two young suspects could still be out there hurting innocent people. >> it's very true. i mean, he put his life on the line. and it worked out for him and got us some real good information. >> reporter: thursday night, a week ago. hours after their photos are released, authorities say the two young suspects kill an m.i.t. police officer and move onto their next victim, a young man known as danny. >> he pulled over to send a text message.

>> reporter: "boston globe" reporter eric moskowitz interviewed danny yesterday. >> he's working on a start up, in kendall square, which is kind of like boston's silicon valley. >> reporter: we walk through the events of that night with brad garre garrett. >> well, the victim described something walking up to his passenger window, knocking on the glass. >> reporter: in what may be the biggest mistake of his life, the young man roms down the window. >> a then this person reaches inside, opens the door and steps in the vehicle. >> reporter: danny is now in the hands of alleged terrorist, tamerlan tsarnaev. two lives intersecting. both men are 26, both immigrants. but within hours, one of them will be dead. tamerlan boasts about killing a cop makes a more chilling remark. >> remember that bombing that happened at the marathon? and the guy said, "of course, yes." he said, "i did it." he then takes his semiautomatic weapon, pulls the magazine out

and shows the victim that he's got bullets in this gun and saying, "i'm serious." >> reporter: forced to drive through the dark streets, they stop to pick up the younger brother, dzhokhar. >> reporter: danny is now carpooling with the two most meedes with n the planet. explosives, including anotr of those pressure cooker bombs. >> and it's not until he sees the younger brother that, "oh, my god, this is the guy, this is the skinny guy with the hair, the one that we've all seen." >> reporter: you have a stranger with a gun who has just told you he committed a horrible act of terrorism and you have no idea what's going to happen next. >> other than you think you're probably going to die. brothers rob him, but he's only got $45 on him, which is not enough. this security camera catches dzhokhar at an atm, using the victim's bank card. danny items "the boston globe"

that during the ride, the talk goes from guy stuff and murderous threats. >> he said that the older brother was gruff and was the one sort of mshg barking at him and the younger brother, he described as more like a student and a little bit sort of goofier and more mar veming at like, wow, this car is really cool, what can your phone do? that kind of stuff. >> reporter: at one point, danny gets a call from a friend. >> danny answers the call, and they say, if you say a word in chinese, we'll kill you. they know he could be saying, i'm in my car, i'm with the brothers from the bombing, call the police. so, he says, in english, speaking to his friend who is speaking mandarin to him, which he would never do, otherwise, saying, i've got to do, i'm sick, i'm staying away from friends. tam eerlan says, "good boy, goo job." >> reporter: do you have a sense of what the brothers' plan was at this point? >> no, and i think the problem is, dan, they never had a plan. >> reporter: this is where police say their carjacking starts to go bad. the getaway car is out of gas.

they stop at this shell station in cambridge, a risky move, because this is a neighborhood where they're known. it turns out to be a decisive moment. so, at this moment, sitting here in this gas station, the carjack victim makes what may be the most consequential decision of his life. >> absolutely. >> reporter: dzhokhar goes in to play for gas. >> now, it's just danny and the older brother. and at that moment, danny realizes that tamerlan has put the gun in the side pocket. he's not holding it and he's playing with the gps. danny realize, now is my chance. just one brother, no gun. i'm going to make a break for it. he does the seat belt, do the door, get out and slam it. he goes, he does it. >> reporter: tamerlan grabs for danny but misses. with the killer right behind him, danny makes himself a moving target. >> he's going to get any shot off, it's got to be over the seat, over the backseat, through the back window and danny's running along the car, between the gas pump and the car,

crosses the street to a second gas station. runs, just, praying that the doors are open because he can see the lights. doors work, he gets inside. out of breath, you know, says, call 911, and runs into a storeroom. >> he says, please, please phone the police. they have a gun. they have a bomb. they want to shoot me. >> reporter: tariq ahmed is behind the counter when danny arrives with his breathless story. he says danny is looking for a place to hide. he ran to the back of the store? >> yes. >> reporter: he realizes if a bomb goes off here, it could ignite the gas station and level this entire neighborhood. >> i took my decision, less than one second. and i called the police. they told me, okay, talk with him. >> reporter: police tell him to put the carjack victim on the phone and almost as soon as he hangs up -- the police is swarming with officers. five minutes, everybody is here? >> yes, five minutes. >> reporter: this is the break law enforcement has been waiting

for. danny has left his cell phone in the car and the mercedes itself has a built-in tracking beacon. they have two ways to track the brothers. once they've been alerted, they start doing just that. they pick up the signal in the nearby subway of watertown. that is where tamerlan is killed, dzhokhar wounded and later captured. what should you do, though, in this situation? what's your advice to people, if you are in a moment like this and you've got an armed person in your car what is the right call? >> you sort of have to marry up your personality and abilities with the situation. >> reporter: victims in other carjackings have taken matters into their own hands with highly varied outcomes. take a look at this tape of a carjacking at a gas station in 2010. there is a baby in the backseat here. the parents run and catch their car. as mother, melanie, latches onto

the side of the moving vehicle, aaron jumps inside. >> i was kicking him and telling him that my baby's in the car and he's stealing my car, get out of my car. >> reporter: the carjacker runs off. baby and parents are fine. and check out this incredible video from tampa, florida. that git in the passenger side is not the suspect. he is the intended victim. >> i kicked him in the head. >> reporter: he happens to be a martial arts expert and puts a hurt on the attacker. >> you have to be reasonable about that. you could get yourself killed by trying something. >> reporter: unlike most carjacking victims, danny, the young man in the mercedes suv, is not just saving himself or his loved ones. his actions had much wider consequences. police now say they believe the brothers were planning to held to new york city to set off more bombi ins in times square. this guy is a bit of an unsung here rope at this point.

>> yes, i think he hasn't really come forward. he hasn't gotten the recognition, but he's certainly played a big role. next -- how do you move forward when the life you know, the life you love, changes in an instant? she found a way. >> i was just like, i'm going to show you i can do it. >> and now she's sharing it with the boston victims. >> 24/7, i'm here. >> surviving and then some. coming up. [ male announcer ] can gravity be used to help overcome gravity? the chevrolet malibu eco with eassist captures downhill energy, unleashing it later to help propel you uphill. it adds up to an epa-estimated 37 mpg highway... ...and helps defy gravity and gas pumps. ♪ that's american ingenuity, to find new roads. right now get a 2013 chevrolet malibu eco for around $169 per month.

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moving on, moving forward. how is it possible after you've woken up in a hospital bed to a doctor telling you that one of your legs is now gone? deborah roberts found out, but also discovered a decredit weapon who has been helping the boston victiming seeing the good the future can still hold. >> reporter: when the smoke cleared last week on boylston street, 264 victims were lying in boston hospitals. for most, the physical scars will fade. but for 16, life will never be the same. jeff bauman's image transfixed the nation. he was rushed to safety after having both his legs blown off.

in an instant, a double amputee. roseann sdoia, seen here just steps away from that infamous backpack allegedly dropped by dzhokhar tsarnaev, is also grappling with the new normal of losing a limb. she'll never forget the explosion and the flying shrapnel ripping into her flesh. >> it was a movie scene. and it was a bad movie scene, very bad. >> reporter: did you know right away that you were seriously injured? >> yeah. i remember the whole thing. i looked down and i saw a pool of blood and -- and i knew that it was bad. >> reporter: for so many, these injuries seem incomprehensible. but not for this north carolina college student. when you heard that there was an explosion in boston, what went through your mind? >> i was just shocked. i really felt for the people that had been injured by it. >> reporter: 21-year-old bree mchan knows about life-changing moments. hers came three and a half years

ago while pursuing her passion. how important were sports, and was soccerour life? >> it was everything. >> i mean, if she wasn't study, she was either going to a soccer game, going to soccer practice or going to see a friend's game. >> reporter: on a september day, bree and her friends were hosting a car wash to raise money for an upcoming soccer tournament. >> i had decided to help my friend, chelsea. because she, like, i really need help, wash my car, i was like, oh, i'll help you. so, i went to, like, stand in front of where she needed to pull in and tell everyone to stop and i told her to stop. her foot slipped off the brake and the car lurched forward. >> reporter: the 3,000 pound car pinned her against the wall, crushing here legs. >> she was squished. all the color went out of her face. there was this look of abject pain. >> i screamed. and then my friend backed off the wall. and then i tried to stand and my knee -- my legs buckled underneath me and i fell.

>> reporter: in a flash, the future bree envisioned for herself, ripped away. >> my friend, chelsea, had me in her lap. she's like, it's going to be okay, it's going to be okay. i was chaos. >> reporter: chaos. and next thing you know you're in an ambulance? >> uh-huh. >> i thought i would be able to save the right leg, but i told them there was no way i was going to be able to save the left leg. and we have to make the decision then. >> reporter: those moments just after surgery, without her leg, are etched in bree's mind. >> it was just shock. i reached down to, like, check out my legs and i couldn't really feel them because i had lost so much nerve and i realized -- i preceded to ask the doctor when i could run again. >> reporter: your next question was, when can i run again? >> yes, after they told me. >> reporter: where did you find that kind of optimism at that moment? >> i don't know. i guess it's the athlete part of you. >> one, two, three --

>> i like proving people wrong. i'm competitive by nature, so, i was just like, see, i'm going to show you. i can do it. >> reporter: roseann is showing that same determination. and like bree, she admits the first days of recovery were dark. did you want to give up for a moment? >> truthfully, yes. i didn't want to live like this. i think that -- i'm a realistic person. and because of my family and my friends, i -- i had to be here. >> reporter: the road back will be long. but bree says the key is setting goals. >> the first goal i ever set was to walk across the field on my senior night. >> reporter: and did you? >> yes, i did. the next one was to make it to college and start being apart of

the team. >> yes! >> reporter: that's right. bree's actually playing soccer again. this time, in a new position as goalie. and bervard even honored her scholarship. >> it meant the world to me that i still had the opportunity. >> bree is absolutely cleared. >> she's never let anything hold her back and this leg wasn't going to, either. >> reporter: now, bree's determined to help boston's new amputees get through their challenges. her message? >> it's not over. you have may not be able to do the same things you used to do the exact same way, but there are still things you can do. >> reporter: astoundingly, bree says she even sees blessings in her accident. >> i think it's made me into a better person. i feel like it's given me a bunch of opportunities that i would never have had before. >> there you go.

>> reporter: opportunities like connecting with roseann, already in rehab and beginning the grueling work of getting back on her feet. >> okay, i'moing to turn this around. i want you to meet roseann. this is bree mcmahon. >> hi, bree. >> hi! >> nice to meet you. >> nice to meet you, too. how are you? it puts a smile on someone's face. wow, like, i can do it, too. if you ever just need a pick me up or just need someone to talk to, i -- 24/7, i'm here. >> thank you so much. >> if i can put a smile on someone's face, i've done my work for the day. [ male announcer ] straight from red lobster's chefs

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but not for long. more summer chillin' to love. well, it is the interview so many around the world have been waiting for. since we first began hearing the name aymmanda knox, the young american college student who found herself at the center of an international murder trial. diane sawyer has the exclusive television interview with amanda. tonight, right here, you get a first look. >> this is the face that became a global obsession. what do you see? a brutal murderer or the victim of a shocking injustice? an american college student off on an italian journey to find herself. what she found instead was a waking nightmare. accused of her roommate's horrific murder. >> did you kill meredith kerr sure? were you there that night? >> amanda knox speaking out for the very first time, after four

years in an italian prison. >> people kent saying, where is the grief? where is the anguish? >> the questions that have never been answered until now. with a new trial looming and her freedom on the line, diane sawyer looks for answers. >> that is an interview you won't want to miss, coming this tuesday night at 10:00 p.m. eastern. i'm elizabeth vargas. >> and i'm david muir. i'll see you this weekend for grabbed in an instant.

a little girl snatched by a would be kidnaper. >> and a problem at a local starbucks. a creepy crawler that turned