this is "nightline." tonight, terror in tennessee. four marines killed in a shooting spree. who was the gunman and why did he target military facilities? what we're learning about the investigation tonight and why authorities are now treating this as an act of domestic terror. plus the miracle survivor. when her family's plane went down she had to watch her stepgrandparents die, then she had to survive for two days alone in the woods. >> yeah i have a lot of burns on my hands. >> tonight she shares her remarkable story, what she did that kept her alive. caught on camera. a motorcycle ride goes horribly wrong. for a firefighter and his friend. >> you're hurt dude! >> tonight we're there as doctors scramble to save his life.

"nightline" will be right back.

we begin with breaking news out of chattanooga. the shooting deaths of four marines. federal officials say they're treating this as a terror attack. tonight what we're learn billion the gunman and his background and how the city is dealing with this trauma. abc's senior national correspondent jim avila has our report on the marines targeted.

an act of domestic terrorism. >> reporter: the crackle of gunfire from a deadly rampage in chattanooga, tennessee. where a lone shooter killed four marines in a hail of bullets, injuring at least three more. >> today is a nightmare for the city of chattanooga. >> reporter: the harrowing ordeal began at 10:45 a.m. a man in a silver ford mustang convertible, his top down drove into this strip mall. there are offices here for all four branches of the military. >> he just pulled up next thing you know he lifted up his arms like this with a big black gun and just -- it was one shot and then it was just endless shots. >> reporter: the shooter fired dozens of rounds. one marine was hit in the leg. >> we heard a loud pop. and so the owner of the salon and i went to the window to see what was going on. >> reporter: but within seconds, the gunman took off, racing the highway

to a navy reserve support center. he entered and started shooting again, killing those four marines. >> all units respond, all units respond, we're treating this as a mass casualty incident. >> reporter: police descend on the scene. and a firefight breaks out. they shoot the gunman dead. >> somebody brutally and brazenly attacked members of our armed services and officers of the chattanooga police department and hamilton county sheriff's office responded immediately. and they were able to make sure that no further loss of life happened. >> reporter: at this point, chattanooga is in crisis. authorities put hospital emergency rooms and local colleges on lockdown. >> this is a very very terrible situation. and we need to go figure out how we can handle it. >> reporter: but 30 minutes after the first shots were fired, it is all over. >> this is a sad day for the united states.

these service members served their country with pride. and they have been the victims of these shootings. we are conducting this as an act of domestic terrorism. >> reporter: authorities have identified the suspect as muhammad yusuf abdul aziz corner in kuwait shown here in a mug shot from a drunk driving arrest earlier this year. we now know the 24-year-old was an electrical engineer with a good-paying job. he was an avid wrestler seen here competing in an amateur mixed martial arts event. in 2012 he graduated from the university of tennessee. his mom proudly posting these photos on facebook. >> we're going to look at the shooter. we're going to do an intense look at him to see if -- what his connections are. we'll look at his friends, family associates, anybody who is associated with him, to determine the cause or the reason why he conducted this

attack. >> to be honest with you, he was like any other kid. he was a wrestler an athlete at the school. >> reporter: his former high school gym teacher was shocked to learn he was behind the ruthless killings. >> it was like a punch in the stomach. until you got to know him he seemed kind of serious. the more i had him in class, he turned out to be a cut-up. he was a joker all the time. >> reporter: sources tell abc news the young man was not under active surveillance bit fbi. a classic so-called lone wolf. the suspect wrote in his 2008 high school yearbook that my name causes national security alerts. what does yours do? >> it is a very very tricky game for law enforcement with lone wolves as to actually know that a, they are there, and b, more importantly that they're going to launch an attack. >> reporter: local police and fbi, desperate for clues, are scouring his home in nearby hixon, tennessee. in a silver mustang he abandoned

at the scene. authorities are also investigating if abdulazeez was inspired by isis or another terrorist organization. >> it is a huge concern. it probably is the biggest concern to law enforcement as far as terrorism is concerned day to day in the united states. >> reporter: as recently as this last weekend, and going back a year isis has been urging its followers in the u.s. to attack uniformed police and military in this country. the group posted photos and home addresses of more than 100 active-duty soldiers saying what are you waiting for? kill them in their own land. >> we are increasingly saying individuals who may be motivated by the ideology of a terrorist group, may be inspired by their social media campaigns, but are acting independent of those terrorist organizations. and that is not a threat that our intelligence capabilities,

as robust as they are, our counterterrorism capabilities as robust as they are, were designed to address. >> reporter: today's attack is eerily reminiscent of past mass shootings that targeted domestic military sites. in 2013 a lone gunman killed 12 people in the washington navy yard. and just last year four people were killed during a rampage at ft. hood in texas. >> attention all units, advising we have an active shoot over ft. hood. >> reporter: it was the second attack on the base. 13 were gunned down there in 2009. in the wake of another senseless mass shooting the nation is on edge. and in mourning. >> it is a heartbreaking circumstance for these individuals who have served our country with great valor to be killed in this fashion. >> reporter: one of the injured that navy sailor is in critical condition. and how many of these makeshift memorials have we seen?

tool. and tonight, it's chattanooga, tennessee, that mourns. dan? >> jim, thank you. we will have much more on this breaking story first thing in the morning on "gma." up next on "nightline," the 16-year-old girl who survived a plane crash and then 48 hours alone in the woods. plus another amazing survival saug garks how quick thinking and unusually capable friends helped save this firefighter's life after a horrific accident. with your man is nice... ...but i think women would agree... ...snuggling up after is kinda nice too. 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. ask your doctor if your heart is healthy enough for sex. do not take viagra if you take nitrates for chest pain; it may cause an unsafe drop in blood pressure. side effects include headache, flushing upset stomach and abnormal vision. to avoid long-term injury, seek immediate medical help for an erection lasting more than four hours.

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first she survived a plane crash that killed members of her family. and then she survived two days all by herself in the wilderness. and tonight a very tough and very brave 16-year-old girl is speaking out to abc's kayna wentworth. >> i was positive i was going to die. then i was positive i was going to live. >> reporter: bandaged hand, burns and bug bites, autumn told an incredible story of survival today for the first time. >> completely white. and then as we were starting to go up i could see the trees and

we crashed and i felt everything vote. >> reporter: for the 16-year-old, the traumatic experience of surviving a plane crash was just the beginning. injured and alone, she stumbled through the unfamiliar and treacherous wilderness of the northern cascades. for two days and two nights she was desperately searching for help. >> we crashed and i was the only one that made it out. >> reporter: her life she credits in large part on survival skills she learned from watching shows like "survivor man." >> this is slick rock country. when that rock gets wet you fall you slip very easily. people die here every single year. >> reporter: it all began on saturday. >> were you hesitant about getting on the flight in the first place? was it something you were nervous about? >> i was very nervous. i mean i've only been on a plane a couple of times before. it was scary for me. >> reporter: at 1:01 p.m. autumn and her grandparents departed kallispell, montana, on their beech a35 aircraft counseled for lnyden

washington. her grandfather was flying. >> he's been flying a long time. it wasn't in his control, it was weather. >> reporter: at 1:10 she texted her boyfriend, if i die, remember i love you. >> there was a little bit of turbulence. i mean i was just kind of joking but i was like this is a really bumpy flight. it was lighthearted. i wasn't genuinely super concerned. i figured they had everything under control. >> reporter: 2:21 p.m. the plane crossed the idaho/washington border. >> we lost complete visibility there was no way to get out of it we couldn't see anything at all. we were just flying and couldn't see anything. we were not above mountains, we were in the middle of mountains. >> reporter: an hour later, 3:21 p.m. the aircraft disappeared from radar 200 miles west near the town of omak. >> we swerved once around a mountain we barely made it. >> reporter: the last cell phone signal from the plane registered nearly a half hour later, 3:49 p.m. in the same area. >> i couldn't see a thing. it was completely white. and then -- i mean i was kind

of anxious and freaked out and scared. i was crouching down. then we crashed. like -- it was completely white, and then there was trees, and then there was fire. >> reporter: investigators say the small plane slammed into the side of a mountain where they discovered the wreckage still smoldering five days later. >> it took basically no time for everything to just -- for fire to start coming out of the front. and that's when i made my way out. >> reporter: her grandparents trapped but alive. she couldn't get to her grandmother through the flames and burned her hand trying to save her grandfather. >> so are you telling me that you watched your stepgrandparents die? >> yeah it's something that's really going to haunt me forever. >> reporter: instinct immediately took over and autumn moved quickly down the mountain. >> i've never felt more vulnerable in my life. it was very steep. i was running off and on. i kept tripping falling. terrain's really rough. so it wasn't easy to just keep going at a steady pace. i was in shock. >> reporter: she followed a creek where she spent the night. >> i was certain that i was

going to die of hypothermia that night but i didn't. i meldheld my knees up to my chest, wrapped my arms around myself pulled my shirt and sweater over myself, and slept like that a ball and used my breath. i woke up that morning and i was completely hopeless. i was just thinking, like -- i was just wishing i had died that night. because i didn't know what else awaited me. >> reporter: on sunday she continued downstream eventually finding a sand bar. the pain and cold started to settle and the bugs came out. >> for us to read that you slept on a riverbank not true? you huddled in fear by a riverbank? >> yeah. i had traveled that entire day. and i slept in the sand bar and got bitten to pieces. by probably sand fleas and bug asks stuff. it was a lot colder than the first night. >> reporter: on monday she kept walking the river, eventually finding a trail. then a highway. help at last she thought. >> i was trying to hitchhike,

trying to get a ride flag somebody down. but nobody would stop. >> reporter: after what felt like eternity two men picked her up and brought the teen to a store where she called for help. >> i have a lot of burns on my hands and i'm like kind of covered in bruises and scratches and stuff. >> she's amazing. she's remarkable. she really had the courage and will to continue on. >> reporter: autumn learned how to navigate this rugged terrain by watching survival shows on tv. >> there are certain things that really stuck with me. like following water downhill. water always goes to civilization. and running water to drink and things like stripping clothes off that are wet. i feel like even just knowing those things definitely saved my life. >> reporter: life-saving lessons that brought a teenager home scared but not without hope and redemption. >> i struggled with things like depression and stuff beforehand. i definitely have never wanted to live more in my life. having a second chance is the best thing that could have ever happened. >> reporter: for "nightline,"

i'm kayna witworth, bellingham, washington. up next another extraordinary survival story. the firefighter in a horrible motorcycle crash all captured on his friend's helmet cam. the lucky twist that may have saved his leg and his life.

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finally tonight, you're about to see a motorcycle ride on a sunny day turn potentially lethal. it's all caught on camera as the driver's friends and then a team of trauma surgeons race to keep him alive. this is a sneak peek of a new

real-life hospital series called "save my life: boston trauma." >> i work with some of the best guys in the world. we're all firefighter similar paramedics with the city of gloucester. >> as firefighters we depend on each other. we have to have each other's backs. >> reporter: it's a crisp october morning in new england. firefighters jason and darrell or a morning ride when something goes horribly wrong. >> jason just took off. there was a truck coming the other way. you know back of my mind i was thinking that i just saw my friend die. >> you're hurt dude! >> reporter: he had almost amputated his leg. >> call, call! don't [ bleep ] move man. >> i'm not going to move. >> chad took his shirt off and tied a tourniquet on. >> we're going to fly him out, he needs to be flown. >> reporter: jason is airlifted to the massachusetts general hospital in boston and time is critical.

>> sounds like could be a bad injury. there's enough energy for them to break a femur, there could be energy enough to cause other life-threatening injuries. >> could we get blood pressure guys? >> it hurts, it hurts, it hurts. >> can you wiggle your left toes? >> i can't. >> reporter: jason is rushed into surgery. >> i don't know if his leg will be salvageable, but right now the primary concern is stopping the bleeding and saving his life. >> reporter: outside, his family waits for answers. >> my heart was pounding because you instantly think, i'm going to have to tell my kids the worst. >> one, two, three. >> reporter: surgery complete his life no longer in jeopardy jason's family is finally able to see him. >> he's okay. can i talk this. >> you can talk to him, it's fine. >> the good news is that we were able to re-establish blood pressure in his leg. the bad news is his leg was

without blood flow for a significant period of time. >> the doctor says you're a tough bastard. you're going to show us how tough you are. >> reporter: it's been five days and jason is in the intensive care unit and he is awake. >> to hear your voice is like so crazy. >> i love you. >> i love you too. >> i missed you so much. >> me too. >> i will never ride another motorcycle again. okay? >> okay. >> they're cool-looking. and guess what you'll never ride? >> a motorcycle. >> reporter: two weeks later, determined to walk and to work again, this firefighter is already up and about. >> it was up in the air i was going to lose my leg for a while there. so no i didn't think i would walk. but i knew i wasn't going to give up without trying to walk. >> reporter: a long recovery ahead but jason is staying positive. >> my job's dangerous. i enjoy helping people.

so i'll always be a risk-taker. and again, it's why i'm a firefighter. >> so that's what i'm working for. for my kids. for me. and return back to a normal life. >> reporter: and you can see much more of jason's incredible story on the new real-life hospital series "save my life" premiering sunday night at 10:00 p.m. right here on abc. we want to thank you for watching "nightline" tonight. as always we're online 24/7 on our "nightline" facebook page and at abcnews.com. thanks again for watching. good night.

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[ doorbell rings ] ray, could you get that? come in! get the door, ray. all right. come in! oh, hello, raymond. hey, there, uh...debra! happy turkey's eve raymond. wah! hey, same to you. deb! oh. hi, mom, dad. you made it. mm-hmm. in record time. your mother kept an eagle eye out for smokies. warren. kids: hi, grandma. hi, kiddies. hi there, babies. oh, isn't this nice? connecticut grandma and grandpa and regular grandma and grandpa. who wants tootsie pops? kids: me! me! me!