gone too soon. as many fight to survive, we meet the cowboy hero who saved lives. and, united we stand. in the aftermath of vicious attacks, tonight from the president to hollywood, support for the city that's fighting back. a special edition of "nightline" -- terror at the boston marathon is just 60 seconds away.

from boston, this is a special edition of "nightline." terror at the boston marathon with terry moran. good evening and thanks for joining us tonight. here in boston on the day after. maybe the most striking thing about this city the day after the bombings is not just that boston is rising up. of course it is. it's a great american city. but that it is doing so under a kind of armed guard. the police presence here is very strong on the streets. in fact, several blocks behind

me there where the finishing line of the boston marathon was, where those bombs went off, they're still blocked off. it's an active crime scene back there. and the presence of the uniformed military personnel patrolling the streets of a great american city. it's a different feel here. but for most people here and around the country, it was the emotions today. flags at half staff. and here in boston, mourning the dead, supporting the survivors, celebrating those life-saving heroes who did so much. they are the focus now that three dead, 8-year-old martin richard, a little boy who loved baseball, was at the finish line to cheer on the runners with his family. 29-year-old krystle campbell and a chinese exchange student whose family asked her name to remain private. they're the focus. as well as the investigation on who killed them. and for that, abc's

brian ross joins us. brian, what do they know? >> good evening, terry. right now, this is an investigation with great urgency because whoever did it is still at large and it's not known whether more attacks are planned. today there was a great breakthrough. according to the fbi, they have recovered the partial mangled remains of one of the bombs that did not fully explode. it turns out it's made out of common kitchen items, a pressure cooker. this exact model that we bought for $140 tonight about a half mile from here. but at a bomb it was palled with wires, electronic circuit board, tiny ball bearings and nails. all designed to maim and kill and get maximum damage to its victims. this is what remains of the pressure cooker turned into a moment made bomb. seen in this fbi crime lab photo obtained by abc news. it was hidden in a black backpack. what's left of it seen in this photo. the simple bombs were responsible for 12 seconds of horror.

cell phone footage shot by a spectator between the two explosions. >> i have have victim here with shrapnel in the leg. >> we need another ambulance down here. 755 boylston. >> they're on their way, sir, they're on their way. i want all the s.w.a.t. teams to go back to the base right now and get their rifles, get their gear. >> reporter: authorities are going through race day videos frame by frame. here the white smoke seen after the detonation indicates a bomb built with low velocity explosive mixtures. unlike a more powerful military grade. >> they may not have the resources as we've seen in other bomb attacks, but they knew how to make the bomb go boom. >> reporter: experts say the large pieces of metal, seen here in the air, suggest the bombs might have been concealed in or under a mailbox or trash barrel, as one witness described. >> i literally saw the garbage barrel explode. i saw the flash, the fire and smoke and ran as fast as i could.

>> as federal agents and police continued to look for the tiniest of clues tuesday at the crime scene, officials said they had learned a lot about the nature of the pressure cooker bomb. >> they have a timer device on them. it appears that this device may have been dropped in a backpack, either inside the trash cans or right outside the trash cans. >> reporter: counterterrorism officials have been warning about the threat of the readily available pressure cookers for years. in 2010, the failed times square bomber tried to use one. an al qaeda internet site provides a step by step manual in how to build a pressure cooker bomb. and this demonstration video from nepal news shows their potential power. >> we find the pressure cooker bombs are used quite extensive in afghanistan and pakistan. so in other words, this is a very similar device to the ieds that we have found throughout afghanistan used to kill our soldiers. >> law enforcement officials say

there is still no solid evidence that links the marathon bombs to al qaeda or to anyone else. but tuesday, there was a new plea for help in trying to identify the bomber. >> any individual who expressed a desire to target the marathon, suspicious interest in researching how to create explosive devices, the noise of explosions in remote areas prior to yesterday which may have been used as tests by those responsible for these acts. someone who appeared to be carrying a unusually heavy dark colored bag yesterday around the time of the blasts and in the vicinity of the blasts. >> reporter: the efforts to learn who is behind the bombing often require great patience and persisten persistence. it took three years and only after the discovery of a tiny electronic part that authorities learned who was behind the bomb that brought down pan am flight 103. the so-called unabomber was at large for 17 years, hiding in the mountains in montana in a cabin before a relative finally turned him in.

in oklahoma city, authorities got lucky. in a few days tracing the debris of the truck bomb and its axle to the rental firm and then to bomber timothy mcveigh. >> what are you looking for here? >> actually, we're going to try to catch everything they probably can think would be tied to the explosive device itself. >> reporter: mike sullivan, former head of the atf, gave me some insight tuesday near the boston crime scene. >> even the smallest piece of evidence we will look at and walk over, they were capture and say that's a treasure trove for them. >> even a little piece like that. >> critically important, it could be the one piece that would tell them exactly how the device was detonated. that might be the only piece that's left. >> reporter: as boston remans a city in grief tuesday with a 15-block crime scene at its center, president obama vowed those responsible would be caught and brought to justice. >> what we don't yet know is who carried out this attack or why,

whether it was planned and executed by a terrorist organization, foreign or domestic, or was the act of a malevolent individual. but we will find out. we will find whoever harmed our citizens. and we will bring them to justice. >> a lot of questions in the beginning of a major investigation. and brian, as if this wasn't enough, there is what appears to be another terrorist scare. this one in washington. what's going on? >> a suspicious letter sent to mississippi senator roger rickart. it had a white granular substance, two field tests indicated it was ricin, a highly poisonous substance. it's been sent to a lab to do full tests and we'll know the result of tests tomorrow. >> it could shake up the delivery of mail? >> it could shake up the

delivery of mail but at this point, there's no indication it's connected to what's happening here. >> thank you very much for that and more on the report on the bombing here. when we come back, we'll tell you the story of that 8-year-old boy, martin richard. killed in the boston blast and of so many others fighting for their lives here. it's our seafood dinner for two for just 25 dollars! a handcrafted seafood feast made to share. first you each get salad and unlimited cheddar bay biscuits. then choose two from a wide variety of chef-inspired entrées like our new honey garlic crispy shrimp or new seafood lover's linguini. round out your seafood dinner with your choice of either an appetizer or dessert to share! don't miss our seafood dinner for two, just $25 at red lobster, where we sea food differently. ♪

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we heard heartbreaking stories of lives lost and inspiring stories of lives saved. by heroes, really, dedicated to doing good. when the worst came to boston, the best came forward. boston grieved today. we all did. a candlelight vigil in the tight knit neighborhood of dorchester for one of their own. a beautiful gap-toothed 8-year-old boy named martin richard, killed at the finish line of the marathon just after getting some ice cream. there is so much love here. >> support and love to help us through. >> reporter: they are dorchester strong and they came out for martin and for his family. who are suffering so much. here, a family facebook photo, his mother denise, recovering now from severe head injuries. his 6-year-old sister jane who lost a leg. his brother henry and his father bill. what does this do for you to be

here? >> if it happened to my family, i know they'd be here for me. >> respect. terrible, awful. especially with the mother and the toddler. awful. >> reporter: neighbors dropped off flowers at the martin home. the clock in the center of town was stopped at the moment he was killed. at a park where he used to play, children scrawled "pray for martin." >> when they announced it, i was like, is it this martin? then when i saw the last name i was like yeah. i thought it was very sad. >> reporter: today we grieved with boston for martin richard. and we learned another name, another of the day at the boston marathon. >> we are heartbroken. >> krystle marie campbell was 29 years old, at the marathon cheering on her friend's boyfriend. she was a manager at jimmy's steakhouse. she took care of her sick grandmother and her dad william campbell told us she was every father's dream. her mother patty spoke outside her home. >> she was all smiles.

you couldn't ask for a better daughter. we can't believe this happened. she was such a hard worker at everything she did. >> reporter: the third victim in the bombing, a chinese graduate student at boston university. her family in china has asked that her personal information not be disclosed. a day of grieving. but there were so many heroes, too. like carlos aradondo. >> you cannot be in that situation and try to help somebody else and run away at the same time. >> reporter: carlos is the man in the cowboy hat. you can see him here in this video moments after the blast pulling away the barriers so emergency personnel could get to the wounded. and in this iconic photo, holding a tourniquet and helping to save the life of jeff bowman who had both his legs blown off. so you saved his life probably? >> i don't know about that. i don't know. i think myself and other people who really respond, that was the

whole purpose, how to help all these people in need at the time. >> reporter: carlos was at the race to cheer on runners, honoring his son alexander, killed by a sniper in iraq in 2004. he was handing out american flags at the finish line. >> this was the flag that i was holding and i drop it for a moment in the ground. and i pick it up and this is how this flag ended up being covered all with blood from the victims. you know? >> reporter: so many heroes, so many lives were saved. dr. george chief of trauma surgery at massachusetts general has barely slept in two days. >> most important injury was lower extremities. completely blown lower extremity off, feet and legs and calf -- >> just blown off? >> completely blown off. patients came here barely alive, having really lost a lot of blood. and it was the rapidity and efficiency of the system that

kept them alive. >> reporter: and emergency room nurse christine landry. she was at the finish line. and even though she's seen a lot in the er, she's having trouble. >> i cried halfway to boston and then i had a really rough time last night. it's just not something you expect to see, even in all my years of experience. i've been a trauma nurse for 18 years. never. >> reporter: when the bombs went off, we knew evil was at work. but so was good. it always is. >> we also as a community and city, we can come together. >> even in darkness, there is light. the people of boston rising up, as i say. boston will rise again. next up, they're going to do it, they'll do it with help. how rudolph giuliani, mark wahlbe wahlberg, so many others are bolstering the spirit here in this iconic american city.

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. >> in 117 years, the boston marathon had never seen a day like it. this race has become more than a sporting event, it's a day to celebrate this city turned into a day of tragedy. the feeling one of hope and

grit, a community bound together and rising up in solidarity both locally and around the country. >> reporter: boston, it is a myth as much as a city. a language as much as an accent. a living organism as much as a slice of geography. whose citizens tend to be so connected to the place that today and tonight lots of them have been phoning home. or the digital equivalent. mark wahlberg tweeting thoughts and prayers with my hometown. comic denis leery, regard for the state troopers and national guard members. they were everywhere. director ben affleck, raised in cambridge over the river, love to our beloved and resilient boston. resilience. after something like this, that is an individual thing. some will feel things getting back to normal ahead of others. a different matter is that of reputation. of boston not wanting to become

best known for its worst day possibly ever. consider all the great associations with that name. ♪ >> boston, the band. there's boston commons, boston general, boston college and university, food called boston, baked bean, cream pie, boston chicken. sports teams called boston. red sox. bruins. celtics. of course, a marathon called boston. what is a city to do when a happy, joyous event gets twisted into a nightmare. there is still going to be remembering. >> people are coming to take pictures of it because there was a bombing here. i mean, it might not be

remembered anymore as the historic boston marathon it's the marathon that had the boston bombing. >> that reality may be harder to shake. boston sports writer and broadcaster. >> we are the hub of the universe, i just don't think this becomes any kind of defining event. it might be associated with the marathon for a long, long time. but it won't be attached to our city. >> and do you know what that is? regular folks, not celebrities, but wheem with lives to live do just that. >> anything else? >> today it was people like michelle who was back at work serving up abbotts frozen custard, now in its 111th year. and this inspector switching tracks for the boston transit trollies. >> one, two, three, team! >> and the mcats, also known as the girl's softball team. it's about not being stopped from getting on.

it's what people do. everywhere after every tragedy and disaster. they will do it in boston. not forget, but not be trapped by a bad memory or a bad monday in april. for "nightline," i'm jon donvan in washington. >> a great american city. thanks for watching abc news. world news now. good morning america tomorrow. we'll have the latest from here. we're all on line. good night, america. blach