>> it is tuesday, april 16th. and good morning. the city of boston is waking up to face its new reality as a target of terror. in a heartbeat the big city event with the small town family feel went up in smoke. shattered by two explosions. >> here is what we know. three are dead, 150 are injured many seriously and investigators are scrambling for answers. >> abc's tahman bradley joins us from boston with the latest. good morning, tahman. >> reporter: good morning, diana, good morning, john. it is a difficult morning here in boston. one of many difficult mornings to come. today resident also put on a brave face and head back to work after their city was shattered by bombs. this morning, the city of boston is on heightened alert less than 24 hours after terror erupted.

thousands were celebrating patriots day running in the city's marathon when just a few yards from the finish line, at 2:50 p.m., the first bomb explodes. >> multiple people down here, okay. i don't know what the cause is. stand by. >> reporter: chaos ensued amid the white smoke, just seconds later, another explosion. at least three people were killed including an 8-year-old boy. more than 140 injured. >> a large puff of smoke and then ultimate chaos, everybody running everywhere. >> i saw quite a few casualties coming back, saw one guy with his legs gone at the knee and some ankles and feet missing. shrapnel wounds to the side of the head. other things, not good. >> reporter: the bombs went off four hours after the start of the race, just 50 to 100 yards apart. first responders rushed to the scene while local hospitals quickly mobilized. some victims were transported by wheelchairs and stretchers, one

hospital official said the scene looked like a war zone. president obama was notified within minutes. he promised action. >> i'm supremely confident that bostonians will pull together, take care of each other and move forward as one proud city and as they do, the american people will be with them every single step of the way. >> reporter: officials are tracking multiple persons of interest including a man being treated at an area hospital as well as another individual who was seen trying to gain access to a restricted area five minutes before the blasts. john and diana. >> all right, tahman bradley live in boston, thank you. well, the fbi is launching a massive effort to find those responsible for the deadly attack. again, looking at bomb fragments and looking at hundreds of videos from the finish line. >> with more, we're joined by abc's devin dwyer from washington. good morning, devin. >> reporter: good morning. the boston marathon attack is the first successful bombing in the u.s. since the september 11th, 2001 attacks. now the full weight of the u.s. government is behind the search

behind who is responsible. authorities this morning are poring over this dramatic video from the finish line for clues. bomb technicians are studying burn marks on bricks and concrete and at hospitals doctors are collecting pieces of shrapnel blasted into bodies. >> and look at the components of the bomb. it will tell them is this somebody that puts this together over the internet or is this a bombmaker. >> reporter: officials believe these were two small and portable devices, possibly hidden in a backpack. one working theory, they were remotely debt anywayed by a cell phone. >> but right now it has all the indicators and every aspect of being al qaeda or al qaeda affiliated attack. >> reporter: so far there are no suspects. though officials are tracking multiple persons of interest including a young man of middle eastern descent being treated at a local hospital. >> we're okay. >> reporter: at the white house president obama urged against a rush to judgment. not using the word terrorism. but he vowed justice for those responsible.

>> make no mistake, we will get to the bottom of this. and we will find out who did this, we'll find out why they did this. any responsible individuals, any responsible groups will feel the full weight of justice. >> reporter: now cities across the country remain on high alert this morning for other possible attacks. officials advise if you see something, say something but they say the best advice is to keep living out your life. john and diana. >> all right, devin, always good advice, thank you from washington for us. devin just touched on this big cities almost immediately went on high alert following the attack. >> here in new york there was an increased police presence throughout the city. cars lined the streets in times square which was itself the scene of an attempted bombing back in 2010. police with bomb-sniffing dogs visible at area airports, as well. and a high alert on the west coast also. in los angeles, police put more patrols to work in the city's transit system at l.a.x. the scene of a failed 1999 bomb

attempt security was instantly beefed up. spectators saw pore security last night at the dodgers game. abc's cecilia vega was outside of the stadium. >> reporter: there is no and has not been any kind of credible threat made to the state of california but it's the attention police are giving to these venues where crowds are gathering is the reason they're on heightened alert out here, not just happening in los angeles but from san francisco all the way down to san diego we are seeing police on heightened alert at sports arenas like we're seeing here in los angeles at government buildings and public transit hubs and shopping malls, airports and los angeles international travelers will be seeing bomb-sniffing dog, extra police and security beefed up. in san francisco, authorities are meeting to talk about an upcoming race in that city, the beta breakers race to talk about security there, all around the state here people are being asked to report anything suspicious to authorities and to be on heightened alert here. >> security concerns extending around the world, as well. especially across the pond in

london, the setting for two major public events this week. >> expect a major military presence at the elaborate funeral of former prime minister margaret thatcher set for tomorrow and police are reviewing plans for london's own marathon taking place sunday. >> when we come back stories breaking overnight include a u.s. military accident in south korea. then more from boston including new videos of the bombing emerging overnight. what is it about this week in april? several major tragedies have all had this week in common. we'll get into that coming up. [ male announcer ] now we can all be at the corner of "just another prescription" and "sweet, something just for me." because walgreens balance rewards is more than a savings card. it's a rewards card that gives you 500 rewards points every time you fill a prescription. points you can redeem in store or online for, well, almost anything. rack up points with each prescription you fill, right here. at the corner of happy and healthy. [ female announcer ] some prescriptions not eligible to earn points.

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and now a quick check on some of the other news we're following. a u.s. military chopper crashed outside north korea. >> the blackhawk helicopter went down on the south korean side of the border with 12 people on board. it appears they all survived the crash. it occurred during joint military exercises between the u.s. and south korea. the cause not immediately clear. and the crash followed the rare public appearance of kim jong-un. the young dictatorpoed up at several events around pyongyang monday to mark the birthday of the nation's founder, his grandfather. he attended musical performances and sports matches as state television continued to fuel tensions making provocative statements against the u.s. breaking news from the heartland. three earthquakes have struck oklahoma. the largest a magnitude 4.3 all were centered to the north and east of oklahoma city. no injuries or major damage have been reported yet. we will, of course, keep you posted as more information becomes available. >> on capitol hill a new immigration reform proposal being introduced today by a

bipartisan group of senators that includes $3 billion to beef up the border with mexico, more than $1 billion to add more fences. the bill would also create a so-called path to citizenship for millions of illegal immigrants who arrived in the u.s. before the end of 2011. meanwhile, the senators who crafted a deal to expand background checks on gun sales appear ready to change it slightly. now considering exempting gun buyers who live hundreds of miles from a licensed firearm dialer. a vote is expected on it by the end of the week. wall street is looking to rebound after one of its biggest losses of the year. the dow dropped 265 points monday following concerns about an economic slowdown in china and the boston marathon attack. gold prices also posted their biggest drop in 30 years but are bouncing back this morning. overnight asian stocks dropped largely due to the slumping oil prices. and in the wake of the boston marathon bombings, the irs is announcing a filing extension for boston area taxpayers.

taxes had been due today because of monday's patriots day holiday in massachusetts. when we come back we return to boston and the search for clues into yesterday's tragedy plus this -- >> i had to think why. i don't understand. >> the runner is fine but her parents are not. her story coming up next.

here are the new details overnight from the boston marathon attacks. an 8-year-old boy is among the three people killed. >> now, police believe the bombs were crudely made devices hidden in bags or backpacks planted in either during the race or right immediately before the race and they believe that the devices were detonated remotely possibly with a cell phone. police have now searched an apartment in a boston suburb in connection with these bombings.

they are also questioning a 20-year-old saudi national but are not calling the man a suspect. so far they've made no arrests. investigators are looking at the hundreds of videos shot by bystanders at the finish line. >> abc's terry moran shows us how this unfolded. >> reporter: boston is one of the world's six major marathons, runners from more than 90 countries. the winner crosses the finish line at 1:10. then at 2:50 p.m., more than half the runners were through. the first bomb explodes just a few yards from the finish line. in the chaos listen for the second explosion just moments later. another angle of the second blast. as people look down the street at the first. >> something just blew up.

go, go. n't know what the cause is.e, stand by. >> reporter: terror turning the boston marathon into a kind of war zone. more than 100 people injured. the youngest victim an 8-year-old boy killed by one of the blasts. >> oh, god, get out of the stands. get out of the stands. >> all of a sudden there was a loud noise and explosion, big puff of smoke and then a few seconds later further up the road away from the finish line a second explosion, a large puff of smoke and then ultimate chaos everybody running everywhere. >> saw quite a few casualties coming back. one guy with his legs gone at the knees and some ankles and feet missing, shrapnel wounds to people on the side of the head and other things. were not good. >> reporter: the bombs went off just 50 to 100 yards apart with a number of cameras capturing the blasts investigators have plenty of evidence to study frame by frame as they hunt for who is responsible.

but by evening, police had replaced the finish line with yellow police tape. >> our thanks to terry moran, incredible images there. hundreds of investigators are on the case this morning with the fbi at the helm. the two many bos were small. portable devices that could have been easily carried in a backpack. investigators are now picking apart every shred of evidence to see if the bombs were put together with information from the internet or the work of a real bombmaker. so far there are no suspects, but they're leaving no stone unturned. >> the fbi and boston police, massachusetts state police will be going over all the videotapes from that entire neighborhood looking to see if there was someone suspicious, if there was someone they recognize doing recognition analysis and running facial software to see who was there and to see if they can possibly trace their movements toward the target area.

>> there are reports a person of interest in a hospital has come under juteny but too soon to tell if he had anything to do with the attack. >> they're looking closely at the timing. this stretch of april is one with a dark history. the nation's worst domestic terror attack occurred on the 19th, the oklahoma city many booing and that's not all. abc news consultant brad garrett say there may be a theme. >> you are in that window of april 15th to april 20 when we've had a number of domestic extremist events, oklahoma city, columbine, virginia tech, some people say that they are driven to a certain extent because hitler's birthday is on april 20th. i'm not suggesting that's connected to this. i'm merely throwing it out that it would not surprise me if this is some local extremist group trying to make a statement because of this particular day. i'm not suggesting the window needs to be narrowed but i would look intensely at what information they had about different extremist groups.

there's a lot of public source information about demonstrations on taxes, on a number of other issues that are hot button issues for extremist groups who don't like either what the government is doing or what the government represents. >> now, some also see significance in the attack taking place on patriots' day in massachusetts. the holiday commemorates the first shots fired in the revolutionary war. >> some of the most harrowing eyewitness accounts of the horror in boston are coming from the runners themselves. more than 23,000 set off in the marathon for many, the crowning achievement of their athletic lives. more than 17,000 had finished by the time the bombs went off. terry moran caught up with one of them, 33-year-old rebecca roach. >> i had a bad feeling when i saw the smoke and when i saw after hearing the noise and hearing the second one, it's the boston marathon, it's one of the world's marathons. it's at the finish line. i suspected it was terrorism.

it was a moment of what should have been joy and turned into panic and just heart-wrenching fears of the worst. >> roche ran with the words mom and dad for her mother and a friend were badly injured by one of those explosions. what new york is doing to show boston its support. >> putting on a brave face. how boston native mark wahlberg is reacting to the tragedy in his hometown. [ male announcer ] it's simple physics... a body at rest tends to stay at rest... while a body in motion tends to stay in motion. staying active can actually ease arthritis symptoms. but if you have arthritis, staying active can be difficult. prescription celebrex can help relieve arthritis pain so your body can stay in motion. because just one 200mg celebrex a day can provide 24 hour relief for many with arthritis pain and inflammation.

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between boston and new york is on the back burner this morning. the brooklyn academy of music is lit up projecting messages of support and solidarity to those affected by the boston marathon tragedy. >> it is so true. new york sports fans and boston fans do not get along but you're absolutely right. this changes everything. at least for the time being. >> you said today we are all bostonians today. >> reacting to the twin bomb attack quintessential bostonian native and actor mark wahlberg says he's disgusted. >> very somber wahlberg was in new york for the premiere of his new movie but says he was so upset by the tragedy he almost didn't make it. and this is understandable. he spends a lot of time in boston. he's from boston and he's always, always talked about his time in boston. >> no doubt. his childhood pal joey mcintyre tweeting a picture of himself at the marathon. then came this emotional tweet. >> he wrote "i don't know what to say. i feel for everybody involved with the boston marathon.

my family is okay. i am okay. gonna take a while to process". >> what do you say, right? wow. >> that really is the case for almost everybody who experienced this especially the ones that were very close to this event. it's going to take them a long time to get through it. >> you'll see it all over the headlines of newspapers no matter where so we figure we'd put a few up from "the boston globe" it says marathon terror and it's a dramatic picture of a woman being assisted on the ground by somebody who looks clearly like one of those brave people who just ran -- a runner who ran towards the danger rather than running away. such heroic stories. >> you know, i worked in boston and worked alongside a lot of these reporters and some of my old colleagues who are still at cbs, the local station there and the people from "the boston globe" and from "the boston herald" they saw this firsthand on boylston street and were there. my old station, they cover it live. here's another headline that you'll see today "terror at the

finish line." my colleagues were at the finish line and their tweets were incredible and saw carnage they never thought they would see reporting this story. >> these headlines not only in america but in papers around the world. >> some of you, local news is next. for everyone else we'll be right back. he'll find someone else. ♪ who's that lady? ♪ who's that lady? ♪ sexy lady ♪ who's that lady? [ female announcer ] swiffer sweeper's electrostatic dry cloths attract and lock dirt, dust, and hair on contact to clean 50% more than a broom. it's a difference you can feel. swiffer gives cleaning a whole new meaning. and now swiffer wet and dry refills are available with the fresh scent of gain. then you'll love lactose-free lactaid® it's 100% real milk that's easy to digest so you can fully enjoy the dairy you love. lactaid®. for 25 years, easy to digest. easy to love.

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flexpen® is insulin delivery my way. covered by most insurance plans, including medicare. find your co-pay cost at myflexpen.com. ask your health care provider about novolog® flexpen today updating our headlines now, an 8-year-old boy is among the three bystanders killed in the boston marathon bombings. more than 140 people were injured. many have undergone amputation. >> investigators believe the bombs were small devices which could have easily been concealed in backpacks. they are questioning a saudi national in boston on a student visa and searched an apartment near boston but have not identified any suspects. >> security has been beefed up at the nation's airports and other public transportation systems. and special attention is being paid to areas like times square and the world trade center site. >> looking at today's weather, expect thunderstorms in south florida, showers from northern new england to pittsburgh. severe storms from the ohio valley down to texas and there

will be showers and mountain snow in the northwest. and finally from us this morning, a closer look at one of the most heart-wrenching images from the boston marathon, the moment terror struck. >> many of us were drawn to the marathoner who was nearing that finish line as the force of the blast knocked him down to the ground and we are happy to report that the 78-year-old runner survived uninjured. abc's linsey davis checked in on him. >> reporter: it is an image that stays with you at the moment of the explosion, bill igfrid knocked to the ground surrounded by smoke just 15 feet shy of the finish line of what would be his third boston marathon finish. >> i could see the finishing ramp. and when i got within about 15 feet of it, this horrendous explosion occurred. i didn't know where at the time. >> reporter: could you see it or just hear it? >> i could see it. >> reporter: approach ed the finish line, 3:50 after he

finished the race in the middle of the pack. he was feeling great until he unexpectedly collapsed. >> my whole body was crumbling like, and i was going down. and, boy, this is going to beat end of me. my last trip. i didn't have any idea what was going on. >> reporter: this 78-year-old then crossed the finish line aided by volunteers and then walked six blocks become to his hotel not sure what had just happened. >> i figured that was some kind of bomb went off. [ explosion ] i didn't really know what to think. >> reporter: so which way was the finish line? this way? >> the finish line was this way. the bomb was behind me. >> reporter: okay. >> yeah. i didn't think about any possibility of another bomb going off up by the start -- finish line, and then after i was up and walking over, then the other bomb went off. it was loud. i mean really loud. and my whole eardrums when i got back, i couldn't hardly here anything. it was tremendous. >> reporter: it's a story of tragedy and triumph for bill,

for far more than finishing a race is happy to be here to talk about it. i'm linsey davis in boston. >> and that is one tough guy just like the city of boston. that's making news in america this morning. we end with a pate