this. >> top of the hour. you're watching special coverage of the terror attack in boston. >> we would like to welcome our viewers in the united states and around the world. >> state and federal authorities look to the public for help. it was two quick blasts, barely 100 yards and just seconds apart killing three and wounding more than 140. you just heard the first blast. here's the second.

>> it could have been much worse. had it not been for first responders already at the scene. >> several of us went running towards the door. two or three of us kept going. half of us went forward and half stayed back. >> what do you see when you get to the casualties? >> lots of smoke and confusion and blood. for me it was just a flash back to iraq.

we had to make room. the marathoners, too. >> surveillance cameras, media footage and cell phone cameras are being searched. cnn has been told that it will be a long, difficult job. >> they will be trying to obtain copies of all of the media, video tapes, the iphone cameras, personal cameras that were being used at the time before during and after the bombings.

you have thousands of people near the finish line. it's going be very difficult. >> let's check in now with peter who is not far from where the bombs exploded. >> on any other week it would be a hub of shopping and activity and is now a crime scene.

they are looking at forensics. there are no suspects or persons of interest. authorities did earlier release a bulletin that was obtained by cnn that said they were searching for a dark skinned male wearing a black hoodie who approached a restricted area and looked rather suspicious with a backpack. but they are said to be on the look out for that person. a town northeast of boston. we have not been tibl really drill down that that was a connection to this bombing. but authorities were there for several hours according to our reporter brian todd, who is out there on the scene.

we continue to see fire trucks. as they start to get to work to figure out why this happened and who might be responsible. >> peter, you were there moments after the blast 12 hours ago now. obviously a very different scene now. even at this hour we are now still hearing stories of those who survived this attack. some terrible first-hand accounts. >> walking over here you bump into person after person who said that, you know, it was a terrifying moment. i saw many people crying. take a listen to just one person who was interviewed after the incident today. >> there was a little girl and

she was screaming and crying and her leg was bloody and she was screaming i need my mom, i need my mom. their instinct is to do what we can. we tell her to come with us but she doesn't want to leave because there is no mom. like i mentioned before, the four of us in a group, three of us physically carried strange children. children we didn't know. we physically carried them six blocks with us to a house we were safe at. and their mother was running behind us with her 2-year-old son. so we had taken complete strangers with us to safety. >> that's a really telling story. this race really was about families and loved ones. people came in from all over the country and the world to watch their brothers, sisters, children, run in this marathon. they came in packs and they were separated because of this.

they were here for hours and hours. >> and simply the number of backpacks and bags. what's happening with those now? >> so many of these runners just didn't finish the race. i actually walked by them earlier and saw piles and piles of bags next to rows and rows of empty school buses there none of those buses ever got used. like you mentioned,

investigators probably want to go through some of those bags, too. i'm certain they're leaving nothing to chance. >> peter, thank you. i'm sure it ease been a long day for you. >> a long day and a devastating afact for the victims and witnesses as well. >> 31 patients in all. some of them critical. at least two of them critical. one of the trauma surgeons described the extent of the

injuries that doctors here are trying to treat. >> the worst of the injuries have been injuries to the legs. there have been a lot of damage so a lot of injury to the muscle. the skin. the bones are broken. it has been a relatively minor issue. >> two of them are in critical condition. those injuries once again. we are being told that -- let me do that again. >> jason carol reporting. a very long day for everyone. >> we have a lot more of that coverage here on cnn.

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>> now for another perspective on monday's attack. this comes from a broadcast journalism student at the marathon who was filming

everything. did i meet you when i was there? >> i actually missed your meeting that you had. i had a class that i had to go to. >> approximate you don't know it's parallel to where the finish line is and where the bomb actually exploded. i was -- i'm doing a package for one of my classes and i was shooting b roll when i heard the explosions. and then suddenly i saw the police barricade the road where the runners are running.

at that point i knew something was obviously going on. i couldn't get very far. >> how were the police dealing with the situation. what was your take? >> well, i thought for the most part they did a very good job. obviously in a situation like this it's tough to be prepared because of the emergency and the hysteria of it. there was a lack of communication in some circumstances. i found that some cops were telling us to go in one direction and others in another direction which created a lot of added stress for some of the people on the ground.

at the same time that's part of like what their job is. >> you needed it in that particular situation. clearly something like this would catch anyone offguard. >> these situations are always confusing at the moment when they happened. i'm curious. what was it like before the blast went off? can you describe what the mood was like? we're focusing so much on what happened after the blast. >> that's really what is so amazing. it was honestly, i went to the boston marathon last year, too. last year was great as well but it was extremely warm today. everyone was very happy. it's difficult when i have to produce a package where everyone is so happy and joyful.

this huge, huge news story and constant massive eruption happened just a couple of minutes later. >> a lot of people helped out and a lot of good samaritans came out. it was not just chaos but a lot of good people helping out the injured and trying to get people to safety. >> yeah, i mean that probably shows a lot about boston's character. i love the city and i love the people. i think the way people reacted and responded to the whole situation really shows a lot about the type of people that we have here.

>> i think i'm pretty much running on fuel right now. you know, it's been tough. but, you know, i think we'll make it through. >> you know people are injured right? >> i don't know specifically who they are because the school has not released the information on their names. but i do know there are seven students that were brought to the hospital. none of them are in critical condition but they were brought to the hospital after the incident. >> isaac moore, thank you. emerson is a great school. >> this is patriots day. it's a very big holiday in boston.

>> before the anaheim angels and minnesota twins game in minneapolis, they held a moment of silence for the victims. listen. >> along with that moment of silence there, the boston symphony was cancelled as well as other. >> president barack obama says he's ordered the full resources of the federal government to respond to the boston attacks. in a statement at the white house he stopped short of calling it terrorism saying authorities don't yet have all the answers.

>> we still do not know who did this or why. but, make no mistake, we will get to the bottom of this and we will find out who did this. we will find out why they did this. any responsible individuals individuals and groups will feel the full weight of justice. full resources to getting to the bottom of whoever carried tout attack. finding out whoever was responsible for this. here is the story. >> expect president obama to be briefed throughout the day today on developments in the investigation. no doubt we will see his schedule start to move to accommodate meetings on the boston attack and he will have to start thinking about going to boston to pay his respects.

to make sure the full resources are made available to investigate this unfolding crisis. the president said he doesn't have the answers we all want. he vowed that the investigators will find the guilty and they will face justice. he did not call this a terror attack. i spoke with the white house official who did. that official told me that this was clearly an act of terror but a thorough investigation will have to determine whether it was planned and carried out by a terrorist group. so the white house is clearly being careful with words here out of an abundance of caution trying to avoid a rush to judgment. >> now thanks to jessica for that report. we will take a short break here. we will talk to a security expert because so many people are asking how do you make these major sporting events safe.

>> can you? can you do it? we'll be right back.

>> welcome back. many security experts say protecting a large outdoor event like the boston marathon is a huge challenge and it just got a lot bigger. >> it certainly did. is it possible to even protect an event like this? >> well, in a very sense? it is very difficult. you can look at isolating particular areas. in terms of proteching it, it would be really difficult.

>> the security plan will be reviewed. >> i think what the police will most likely be considering within their planning for the marathon will be the protection of the competitors, particularly at the start point. any terrorist that is looking for mass casualties would be looking for the largest number of casualties they can achieve. >> it's a 52 mile area that needs to be guarded by security.

do they have to re-think everything now? >> i think to a certain degree there is only so much that they can do. i know that there are protective measures around the start points. showing that those can startle commence on that area. but on the second side of it, immense if you like string, they have to secure. no doubt we will see here in any police or emerging success. any pack a.m.s and backpacks that are left unattended. that is a major part of that effort. >> it does remind me of the days

after 911 that when they said if you see something, say something. >> we'll be right back. these cool sliders. what's this one do? i dunno. the name's bear, fancy bear. score planner is free to everyone. free score applies with enrollment in freecreditscore.com fancy bear slider still in beta.

>> and we now have a name for at least one of the victims of this terrorist attack. they are reporting that

8-year-old martin richard was killed. his mother and sister were also seriously wounded. and this is the moment when the explosion occurred. this video was taken by a boston globe journalist who was at the finish line. take a look.

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. >> security is intensified across the u.s. an investigation is underway. joe johns is in washington and explains how different federal departments are working together in the investigation. >> in boston, the federal

response has been enormous. the fbi which takes the lead roll is flooding the city with assets to process an enormous crime scene. the federal bureau has sent every available person from new york. they have activated their national response team which is made of of certified explosion specialists and k-9 handlers. everyone has said these devices did not appear highly sophisticated but they were very powerful. they will be looking to figure out what they can learn from the ark of the explosion. all to help agents discover whether it was the case of home groan or international terrorism.

mass transit including subways and airports getting a close look right now. the tighter security appears to go up and down the east coast, as far as south as miami and as far west as san francisco and seattle. of course it is just about as tight as it can get in the city of boston, itself. police there are on emergency deployment. john farahs, cnn washington. >> we have been reporting that there is a lot of police activity in revere, massachusetts. that is not far from boston. about five miles. >> brian todd is there. he joins us on the line now. what are you seeing? >> we were told by a massachusetts state police

official there that they were checking out one apartment in the building. police were there for several hours. there were massachusetts state police and revere police there. a neighborhood told us they had been there since at least 5:30. they left, we believe, the last of the police officials left at about 2:00 in the morning. so, we, you know, we were there outside the building pretty much the whole time. they would not talk to us and tell us exactly what they were doing there. two gentlemen came in who they did question. that's about all we can tell you. that's what we saw through the lobby.

and they were checking out one apartment. but whether this is a heart connection to the case we're not sure right now. >> do we know exactly what they are looking for? this suspect if this is actually a solid lead. >> they did not lead with anyone. we asked if they made any arrests they wouldn't say. >> so it could have been to question some people. . maybe someone who acted suspicious may have been from there. with a state police presence and possibly a federal one as well.

>> okay. brian todd on the line. we have to be so careful in reporting all of this. >> they have been very particular of saying no person of interest. no suspect. just talking to people trying to figure out exactly what is going on. but again, no official suspect. no person of interest. >> if you look past bombings, the world trade center, the atlanta bombing, oklahoma city bombing, it was a long time before there was a suspect. >> we will be back. we will check some of the other headlines on the other side of the break including the situation in north korea. #%tia[

>> it was just this huge pile of smoke. and then it sounded like a huge cannon going off and another one just happened right across from us. it was just a huge explosion and there is debris everywhere. >> a big huge explosion while we were having lunch and everybody ran for the doors and windows and shelter under tables. >> the elevator shook the whole building. >> these explosions occurred 50 to 100 yards apart. each scene resulted in multiple casualties. >> the explosion looked like it was right beside the finish

line. >> this all happened with the -- >> many, many people injured and those injuries are severe. there was a lot of blood left at the scene. >> we helped picking up people and putting pressure on wounds. a lot of people were hurt and we ran as fast as we could. >> they were banged up. bad. severe lacerations. amputees. a lot of shrapnel. pretty big explosions. >> make no mistake.

we will get to the bottom of this. we will find out who did this and why. >> the attack came without warning and without mercy. an 8-year-old boy is among three people killed when one blast was followed just seconds later by another. and the death toll could rise. 140 people are wounded, many of them critically. many victims were hit in the legs with shrapnel and several amputations have been performed. the president says those responsible will feel the full weight of justice. we're learning the security plan for this weekend's london

marathon will be reviewed in light of the deadly bombing. organizers say they expect the race on sunday. >> and we will have more on the terror attack in just a moment. we would like to take a look at other news from around the world. this just in to cnn. the u.s. military says one of the helicopters, which is a transport chopper has crashed near the north korean border, calling to the u.s. military, this is a marine chopper. it went down. no word on the cause. >> retall tory action will start

without any notice. that's in response to what it calls insults from authorities in the south. >> those insults apparently include this rally on sunday. monday was the 101st anniversary. it is the most important holiday on the north korean calendar. >> made clear their feelings about kim jong un and burned epys.

>> what makes this protest particularly potent is the day that its happening. the most important day for north korea. >> april 151 a national holiday. the day that kim ill sun was born. the grandfather of kim jong un. the leader reverently paid his respects to his ancestors. displayed before north korea's most popular girl band. all of this displayed with absolute blind devotion. >> why is that devotion so important? >> that's all north korea has.

if it doesn't have devotion and political support it can crumble from within. >> north korea watcher jasper kim says that's why. when you compare kim ill sun, you can't help but notice a resemblance. >> what can you do? how do you mitigate the risk? well, i think one tactic is basically to make the third generation leader look like the first generation leader. >> on the day his country celebrates its founder, kim jong un has proven he is not his grandfather. >> he's younger and more aggress if. what we know so far is every move he makes it's in bold strokes and high risk, high reward. >> inside korea, is there a sense that this crisis is over? >> it's note over. it's just the beginning. this is not one of those things

where a crisis starts, gets hot and cools off and ends. there is in this end to the story. >> there was a big sell-off on wall street. how is asia reacting to that now? >> initially at the morning session today we also reacted with a big sell-off. the markets have erased some of their losses from just a couple of hours ago. in the last two hours, they have reversed directions after spending most of the session in negative territory. let's take a look at the big board. as you can see, most of the indexes are still in the red. some of them have closed already. the big factor that weighed down the markets today and yesterday was first quarter gdp data. that data showed that growth in

china slowing to 7.7% in the first quarter compared to the last quarter of 2012. trading now at $99.67 a barrel. and another commodity is gold. and the price of gold is still below $100 an ounce even though it has hissen to about 13.75 an ounce. the boston bombings are not having a direct effect.

the bigger issue of national security and uncertainty is something investors will certainly keep an eye on. >> they always do. thank you for that. live for us in hong kong. i don't make any decisions about who to hire without going to angie's list first. you'll find reviews on home repair to healthcare written by people just like you. with angie's list, i know who to call, and i know the results will be fantastic. angie's list -- reviews you can trust.

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>> authorities are on the lookout for somebody described as a black male with a possible foreign accent. he was seen with a black backpack trying to get into a restricted area. three people were killed including an 8-year-old boy. more than 140 were injured. >> severe lacerations. amputees. a lot of shrapnel. pretty big explosions. a lot of blood everywhere. >> tributes have been pouring in. conan o'brien mentioned the attack in his opening monologue. >> we do have a great show for you tonight. >> good show. >> but i did want to start by mentioning what an upsetting and sad day it has been.

i'm talking of course about what happened in boston earlier today. boston's my hometown. it's where i grew up. it's where my family lives and i wanted to take a moment that my thoughts and prayers are with the people of boston and everybody who has been affected by this absolutely senseless act. it's important to say right up top. that said, it is our job to do a show and we will try to entertain you the very best we can. given our track record gives you people a 0% chan20% chance of h good show. >> and ben affleck tweeted earlier saying such a senseless and tragic day. my family and i send our love to our beloved and resilient boston. >> you have been watching our special coverage of the