These men suspected to be behind the violence. The exhaustive search for answers and the one who may have got away. Was this latest Terror Strike sparked by the capture of europes most wanted man . The investigation intensifies. Announcer this special edition of nightline, brussels under attack, will be announcer this is a special edition of nightline, brussels under attack. Good evening. Thanks for joining us. Brussels on alert tonight. The headquarters of nato and the European Union still reeling after a brazen terror attack on that city. A series of deadly bombs, at least one packed with nails, killing dozens. Injuring hundreds at transportation hubs at the height of rush hour. Here at home the u. S. Stepping up security and issuing travel warnings for europe. Millions on edge bracing for what might come next. Abcs chief Foreign Correspondent terry moran is in belgium for us tonight. Its okay. Reporter a routine morning became the scene of carnage. Stay down. Stay down. Reporter as brussels, known as the capital of europe, became the target of two separate terrorist attacks. What it was, a truck or bus. It was a terrorist. Reporter twin blasts hit Brussels International airport, filling the terminal with smoke and shattered glass. Big bang. Everybody cried and came along here. You saw kind of smoke, you know. Reporter and then an hour later another explosion at the Maalbeek Metro station. Isis has claimed responsibility for the deadly terror attacks that left at least 31 dead and at least 250 injured. Tonight, 15 local hospitals are treating the victims. This nail was recovered from a victims body, possibly indicating a nail bomb was cuesed in cues ed used in these attacks. The terror started at 8 00 a. M. In the departures terminal of brussels airport. There have been explosions in the terminal hall. Reporter two bombs exploding just minutes apart. One near Airline Baggage counters and another by a Law Enforcement later found a third bomb in a suitcase that never detonated, leading them to believe the first two bombs may also have been in suitcases. You just feel like a wave, a wave go through your body. Smashed windows. We didnt get any information. Reporter the terminal filled with smoke and the sound of screams. Travelers lying on top of each other on the floor. This man holding a little girl. Stay down. Stay down. Reporter people huddled in fear and then the questions. What it was, a truck or was it a terrorist . Reporter this man picked a small baby up off the floor before running to safety. The bombs so powerful ceilings collapsed. Airport security scanning for victims. You have to go, sir. Reporter ordering people to evacuate, they rush out of the terminal. Glass crunching under foot. Hundreds of people started running. I ran with them. There was no clue as to what was going on. Reporter outside, smoke pouring out of shattered windows as terrified travelers run away. About an hour after the airport blasts another explosion about seven miles away at Maalbeek Metro station. A bomb tearing through a fivecar train packed with rush hour commuters. Everyone started screaming and people dropped to the floor. People were crying. Reporter american Brian Carroll was on that train. Collectively, we all manually forced open the door, and at that moment i looked at, you know, the platform and thought, probably it makes sense to get off. But at the same time if i get off the platform whats waiting for me on the other side . Are there terrorists there that are going to shoot everyone as they get off . And we just decided to go for it and get off the train and try and find safety. Reporter one metro stop away screams of a child. Survivors helping each other out of the subway cars and walking into dark tunnels to escape. [ screaming ] this man still clutching a bouquet of flowers. Details are beginning to emerge tonight about many of the injured, including belgian professional basketball player sebastian belin. He had to stay on the floor for about an hour. So he lost a lot of blood until he was finally transported to a hospital. Reporter and then theres chad and kimberly wellss son, who was burned and hit by shrapnel but able to call his parents today from his hospital bed. But your eyes are okay . Yeah. My right hand is also kind of badly burnt. Okay. But it should be fine as well. Words cant describe the joy and the relief that we felt to hear his voice and know that he was alive and okay and hes going to pull through this. How long will you be in the hospital . A couple weeks. Oh. Reporter hes had a history of close calls. Wells was a block away from the Boston Marathon bombing three years ago. And he was in france during the paris attacks in november. Now this. He was extremely close to the blast. Therefore, he got burned by it. Its a miracle hes alive. Reporter now investigators are trying to find the people responsible. This photo shows three possible suspects from the airport attack. According to the belgian federal prosecutor, two of the three he says are likely suicide bombers. An urgent manhunt is now under way for one possible surviving suspect. The manhunt triggering raids across brussels. Guns drawn, a drone overhead. Police move in using a camera on a stick to peer into an upperfloor apartment. These people evacuated through a window. Residents gathered to watch. They did not allow me to go inside or even outside, this man said. The People Living there cannot go out. The sweep lasting deep into the night. The raids have targeted this neighborhood just a mile or so from downtown. This whole block has been cordoned off. And they have found yet another explosive device packed with nails, chemical products, and an isis flag. Tonight, authorities are investigating whether todays carnage was triggered by this raid four days ago. The one that took down Salah Abdeslam, the missing attacker from the paris attacks last november. Abdeslam allegedly rented the car that carried a group of terrorists to this soccer stadium. [ explosion ] abdeslam also rented the car that dropped off the isis gunmen at the bataclan theater where an american rock band was playing to a soldout venue. Four men brandishing assault rifles opened fire on the crowd. The most wanted man in europe all the while apparently hiding right under the noses of belgian authorities. He evaded them for four months until they found him in this apartment only a few yards from his family home. Abdeslam is believed to be the man in the hooded sweatshirt being dragged off a pavement by police, shot in the leg. You can see him limping as they force him into the car. Special forces searched the nearby buildings with their guns drawn looking for accomplices. Authorities say in custody abdeslam cooperated, admitting to planning other attacks, all while hiding in molenbeek, a neighborhood known as a hotbed of extremism. The streets of this neighborhood are full of arabic restaurants and grocers and butchers, and its one of the neighborhoods that has sent more jihadi fighters to syria and iraq than any other place in europe. Three of the alleged paris attackers were from here and of the more than 500 belgians believed to have gone to fight for isis many have links to molenbeek. Today brussels has declared three days of national mourning. And the world is rallying behind them. Manuel valls, saying we are at war. And president obama reacting to the terrorist attacks from cuba this morning. We stand in solidarity with them in condemning outrageous attacks against innocent people. We will do whatever is necessary to support our friend and ally belgium in bringing to justice those who are responsible. And this is yet another reminder that the world must unite. Reporter for nightline im terry moran in brussels. Up next, what authorities are learning tonight from this grainy surveillance photo in the rapidly shifting investigation. New late details on the manhunt from our brian ross. Olay regenerist renews from within. Plumping surface cells for a dramatic transformation without the need for fillers. Your concert tee might show olay regenerist. Olay. Ageless. And try regenerist microsculpting eyeswirl. It instantly hydrates to plump and lift. If you have moderate to severe Rheumatoid Arthritis like me, and youre talking to a rheumatologist about a biologic. This is humira helping to and protect my joints from further damage. This is humira helping me reach for more. Doctors have been prescribing humira for more than ten years. Humira works for many adults. It targets and helps to block inflammation that humira can lower your ability to fight infections, including tuberculosis. Serious, sometimes fatal including lymphoma, have happened, as have blood, liver and nervous system problems, serious allergic reactions, and new or worsening heart failure. Before treatment get tell your doctor if youve been to areas where certain fungal infections are common, hepatitis b, are prone to infections, or have flulike symptoms or sores. Dont start humira if you talk to your doctor and visit humira. Com. As investigators across brussels sift through the smoking wreckage for clues, one chilling image, a grainy surveillance photo of three men dominating the International Manhunt for one key suspect. And late details tonight on what may be triggering this latest onslaught of terror. Heres abcs chief investigative correspondent brian ross. Reporter the key to the investigation tonight is this photo and the surveillance videos it came from. Three men looking grim and determined as they push luggage carts through the brussels airport. Now identified by belgian authorities as the suspected attack team. Their names provided to u. S. Officials late today by the belgians. The belgian authorities are going to be going through every one of those videocameras and seeing where these people are throughout the airport. Was there maybe somebody else in fact who who was with them and broke off. Reporter two dressed in black with no effort to hide their faces are believed to have been the suicide bombers. Their bombs hid nen their large bags according to officials. Each wearing a black glove on the left hand, perhaps to hide the bombs trigger, according to one former fbi official. Whether its wires, strings, a button. Something is there that when they move their hand it actually makes the bomb go off. Reporter the third man who Authorities Say got away and is being sought tonight has a hat pulled down over his face. Pushing what may have been the third bomb that Authorities Say did not detonate. The other individual could be their handler. He wants to be able to live for another day, for another terrorist attack. Reporter bomb experts tonight are studying the aftermath of the devices set off at the airport. But already they say another one appeared to be much more powerful than the explosives used in paris last november. This xray of one of the victims shows how the bombers used threeinch metal bolts as shrapnel, tearing into human flesh at a speed of one mile a second. No other reason but to kill and maim. Hopefully the blast wave would knock them unconscious because its devastating. Reporter and authorities believe it all represents careful planning and Stealth Operations by the isis Central Command in syria. Over the last year hoping to establish sleeper cells across europe and the u. S. We know that isis created an external attack Division Last year that they created within that Division Units for each country. People who were from germany. People who were from england. People who were from the United States. Reporter and of course from france and belgium. Unfortunately, there are maybe cells that were kept separate intentionally from this unit. Cells that the first cell did not even know about may still be out there. Reporter and belgian authorities fear that the capture last friday in brussels of the longsought fugitive from the paris attacks Salah Abdeslam may have triggered tuesdays attacks. As soon as members of the cell knew that abdeslam had been captured, they knew he would be going under interrogation. They knew the papers and the analyzed. That probably told them immediately go to ground, hide, get ready to do an attack. Reporter members of congress say they were told much the same thing about abdeslams arrest at a classified briefing late tuesday. And in fact that arrest still may have saved lives because it may have been even more lethal if they had the luxury of more time to plot and plan. But i wouldnt be a bit surprised if the timing was reporter security in the u. S. At major airports and Transit Centers was stepped up today amid fears the attacks in brussels could trigger attacks in the u. S. This is something he with think about every minute of every day. Reporter it certainly triggered some terror jitters, as we saw at new yorks Grand Central station. Keep your eyes open, watching whats going around. Weve seen a lot more Police Presence. Always aware of my surroundings. Look left and right, up and down. We hope that, you know, the powers that be are doing what they need to do. Reporter officials were taking no chances. A flight that took off from brussels just before the attack landed in orlando, where it was met by a heavy Police Presence far from the terminal. It was cleared after an inspection of the baggage. And in denver part of the airport terminal was evacuated after a bombsniffing dog alerted on some baggage. It too was later cleared. But there are legitimate concerns given what happened in brussels. This is a completely unsecured area. Always has been, right . Completely unsecured. Security official john cohen told Abcs David Kerley that the areas before Airport Security are especially vulnerable. Weve built up checkpoints and screening procedures and screening technologies. But the front of the airport is vulnerable. Someone can walk in the door with an explosive device or a firearm and can create a lot of havoc and a lot of injuries with people who are waiting to go into the other part of the airport. Reporter at present u. S. Officials say they know of no socalled isis cells in the u. S. But the fbi continues surveillance on dozens of americans in all 50 states who have shown alleged sympathies for isis. In the past 2 1 2 years, 103 americans have been charged with trying to join isis or are suspected of supporting the group in some other way. But still, its far less of a problem than exists in many european countries. The number still is relatively small. And the reality is that the muslimamerican communities here in the United States are not as isolated, not as alienated as what weve seen in certain places in europe like this neighborhood in brussels which was very difficult for the police to penetrate. Reporter for nightline brian ross, abc news, new york. And up next, join us on a journey of images. Some of the most unforgettable moments weve witnessed on this tragic day. Red lobsters lobsterfest is back. So come try the largest variety of lobster dishes of the year, like lobster lovers dream and youre invited. So come in while it lasts. If your family outing is magical for all the wrong reasons. You may be muddling through allergies. Try zyrtec for powerful allergy relief. And zyrtec is different than claritin. Because it starts working faster on the first day you take it. Try zyrtec. Muddle no more. Your heart loves omega3s. But the omega3s in fish oil differ from megared krill oil. Ed is easily absorbed by your body. Megared. And finally tonight, as the smoke clears in brussels and the chorus of whys intensifies we take stock on this terrible day. The heartbreak, the the moments that will linger in our collective memory. Tonight, iconic landmarks around the world alight in. Awash in the colors of a nation bruised but not broken. Those grieving in brussels in the streets with messages of unity written in chalk. A temporary tribute to lives gone forever. And in cuba president barack for global solidarity. This is yet another reminder that the world must unite. We must be together regardless or race or faith in fighting against the scourge of terrorism. Reporter in our American Flag lowered to half staff. I want you to all sing it with me. Reporter in london adele offering this moving tribute to the victims. Performing make their honor. And in france, a cartoonist for lemonde with a simple message. Paris and together in a somber similarity. On social media the hashtags ray for belgium shared all over the world. There was a massive explosion. The lights went out. The power went out on the train. Everyone fell to the ground. It was clear to me at least thatrist attack. Reporter millions heard the voices of those who lived through the harrowing hours. I felt it. I can still feel it in my chest blast. Reporter recounting the horrific moments when survival was uncertain. It was a nightmare. The Worst Nightmare you could imagine. Reporter but perhaps more importantly, the true nature of can shine bright in the darkest times. It was really this sense of humanity that emerged in this sense of me shows that these types of things dont defeat the human spirit. For the latest on brussels, tune in to gma tomorrow. And as always, were online at on our Nightline Facebook page. Tonight our thoughts are with the victims, the survivors and those struggling. Coming to you from hollywood, almost live, its comics unleashed with your host byron byron welcomes andre hernandez,