A worldwide terror crackdown under way. The target, one mastermind and the Terror Network behind the paris attacks. More than 150 raids, dozens of arrests. The president of france declaring war on isis. Launching air tribes. But there is skepticism at home about Syrian Refugees as isis issues new threats against america. Abcs chief Foreign Correspondent terry moran is on the ground in plus sells. Brussels. Reporter warnings of more attacks on u. S. Soil issued by isis militants in a batch of new propaganda videos saying, as we struck france in the center of its abode in paris, we swear we will strike america at its center in washington. Cia director brennan says the attacks in france should serve as a wakeup call for americans. Their agenda is to kill. Pure and simple. Reporter the threats come after the u. S. Helped france organize an air strike that pounded the de facto isis and today the noose tightened around the isis fighters responsible for the carnage in paris. Seven attackers confirmed dead but at least one remains at large. 26yearold la saw abdel slam, now perhaps the most wanted man in the world. A French National born in brussels hes believed to be the gunman who led the Team Shooting in restaurants and bars that left bodies out in the open streets. This Morning Police thought they tracked him to this building in the gritty neighborhood outside brussels molenbeek. Police cordoned off streets, surrounding an apartment building, scaling rooftops. Then they moved in. But their target was gone. Police say he fled paris friday night. They found the cars hed rented. One left outside the theater, the other abandoned in this suburb. Then driving a third car with two other passengers, he headed toward belgium, stopped by police at a roadblock on saturday morning but not detained. The two other people in that car picked up by police later, now charged with participation in terrorism. And the fugitives brother detained but later released saying he had no idea that both his brothers one died during the attacks were terrorists. We are an openminded family, we never had any problem wills jut advertise. We do not know if he will have the courage to turn himself in. He you up here, he is a normal person. Abdel slam is among muns in belgium who have joioid isis or other terror organizations. A fert ground for extremists. We spoke to a resident whos seen this firsthand. Three of your neighbors went to syria . Right. Reporter after 12 people were killed by three gunmen in the Charlie Hebdo attacks, in paris this past january, authorities traced the rifles used back to belgium. Link in past plots. Hasan rahali is a city councilor here. Is it a cancer or disease in this neighborhood . Its a disease now. Its become a disease. Reporter he tells us how discrimination against muslims may have radicalized many young men. There are things that remind you youre different. Youre coming from somewhere. Youre second. Theres the first level and the second level. Second chas . Second class. Thats really the problem. When you were young and you felt the sting of discrimination, when you felt the pain hopeful, hopeful. You know, this desire, desire to beat. Desire to make something bad. You are so the frustration in you, you need to expose it. You felt that . Yeah, absolutely, in my heart. Deep in my heart. Massacre, officials now cracking down on these jihadist hotbeds. In france, 168 police raids took place. In all, 31 weapons and computers seized. 23 people have been arrested and questioned. Another 104 placed under house arrest. Authorities believe the plan was organized in belgium, carried out in france. But masterminded in syria by this man. 27yearold abdel hamid aboud, linked to previous terror plots including the foiled european train attack earlier this year. Isis is much larger than al qaeda ever was. And certainly much more powerful today than al qaeda is. They are more well trained. They are more well funded. And they control much more territory than al qaeda ever did. Reporter isis is believed to have 20,000 to 30,000 fighters financing their terror. Oil fields that generate about 40 million a month. The group signaling to the world that its operating on a global scale, prompting frances president Francois Hollande to order the countrys biggest raids in syria to date. The targets an isis command post, training camp, recruiting center, weapons warehouse. Areas the u. S. Identified and passed along to france. We are at war with jae haddist terrorists, hollande said. In the last 15 months the United States conducted the majority of the more than 8,000 air strikes in iraq and syria, committed 3,500 troops to iraq, and 50 u. S. Special operations troops. But critics now say its not enough. Earlier today president obama responding to multiple questions about his strategy against isis. There will be an intensification of the strategy that we put forward. But the strategy that we are putting forward is the strategy president obama, after the paris bombings, seems intent on doubling down on a losing strategy. Thats not going to work. A few more air strikes are not going to eviscerate a group as determined and as entrenched as the islamic state. We need a new strategy to mobilize the sunnis who form the Popular Support base for isis. We need to turn them against isis. As we previously turned them against al qda in iraq in 2007. Reporter the attacks, the new threats and reports that one of the paris attackers may have slipped into france as a syrian refugee have forced the u. S. To ramp up security. A growing number of states are now refusing to take in those refugees. Potentially affecting the 18,000 cases referred by the u. N. For refugee resettlement. We cant be in a position where we abandon our belief in refugee asylum because of the possibility that there might be one terrorist hidden in the group. We have to do very thorough vetting and if they cannot be fully vetted theyre not allowed in. This country stands for taking in refugees and asylum seekers. And for us now to abandon that is to do exactly what the terrorists want us to do. Reporter while cities across the u. S. Are now on high alert in new york city a heavy Police Presence in times square. Beer here to prevent, detect, deter, disrupt. Reporter concerned after the paris attacks. For nightline im terry moran in brussels. Our thanks to terry moran reporting from brussels tonight. Were joined by abcs chief justice correspondent pierre thomas. The Intelligence Community is clearly concerned that the jihadists seem to plot the attacks undetected. Juju, there are real concerns about whats called the growing dark syndrome. Officials worry the killers in france may have used Encryption Technology to hide their computer and cell phone communications. Suspect the terrorists used Gaming Systems like playstations to communicate off the grid. All disturbing because it appears the bad guys were invisible. Thanks, pierre. Deeply disturbing. Pierre thomas in washington. Up next the dramatic survivor stories emerging from paris. Fact. Advil pain relievers are used by more households than any other leading brand. To treat their aches and pains more people reach for advil. Relief doesnt get any better than this. Advil. Ok, were here. Heres dad. Mom. The twins. Aunt alice. You didnt tell me aunt alice was coming. Of course. Dont forget grandpa. Can the test drive be over now . Maybe just head back to the dealership . Dont you want to meet my family . Yep, totally. Its practically yours, but we still need your signature. The sign then drive event. 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What a cosmopolitan city like paris does best. Romantic outdoor cafes, soccer match, a rock concert. All shattered by terror. Tonight powerful stories and images of survival emergeing amid the bloody chaos. Abcs matt gutman is in paris tonight. Reporter its been three days since paris rupted in gunfire. The worst across the street from here at the bataclan theater. As parisians continue to mourn the survivors, initially too traumatized to speak, are beginning to tell their stories. The crowds raising a glass to the band. Jamming delightfully away until the music stopped, replaced with shots. Not automatic but just semiautomatic . Yeah. Bang, bang, bang. Then again the recharge. Reload . Yeah, reload. Reporter celia and benjamin were on date night. Listening to the eagles of death metal as murderers in the form of three isis suicide attackers emerged from the back. We saw blood ever everywhere. People next to us bleeding. So we were all lying on the floor. Just trying not to move. One of them so they were mostly i think three of them young people, around 20 years old. Reporter eight rows from the stage, another group of 20somethings, hannah and jack. Jack stepped to the back and looked to the gunman, looked to the front. I could see the lead singer. His face just dropped. Reporter they fired as they went. Dispassionate. They started shooting. Shot shot shot shot shot shot shot that for ten minutes without stopping. Reporter some were able to immediately flee to the exit. Behind the seats. My friend was behind me. And he ducked. And i said, theres a safety exit, lets go. I took my friends hand. Kind of hike inched your way over . Yeah. I didnt stay on the floor. Stupid of us. Could have gotten gunshot, i suppose. Reporter celia and benjamin were pinned down, forced to play dead among the dead. There was bleeding on my feet. I felt the blood dripping on my feet. There was another one lying on blood, big blood. An ocean of blood. Reporter these are the faces of the men and women in that crowd friday night. And in the aftermath, youa picture too grisly to show without blurring it. The attackers issued no demands but stated their purpose. One of the attackers said, you killed our brothers in syria and now we are here. Another one said, dont move or i kill you, and he started again. Reporter those inside desperate to escape. Jack and hannah saw an exit. Just to see people crawling along the floor. Three layers of people that froze or tripped and they werent moving. You had to climb over these people. That was the hardest thing. That you were pushing down on someones shoulders or standing on someones back. Reporter they spill out of the theater into this back alley. This man hobbling away. Dragging the wounded. And there on a ledge a woman hanging. She cries out please, please, mister, ill pregnant. A grainy figure begins to pull her up as the camera pans away. Sebastian is a 34yearold musician. Abc news has learned he saved her but didnt know it until after the shooting. The butchery so savage not even those in it could comprehend it. I didnt know what was happening. Its only afterwards when we got home in a cab, we sat in front of the tv, we saw the messages that i realized it was an actual terrorist attack. Reporter back inside, celia and benjamin had lost each other. I could see her but i couldnt touch her. I didnt know if she was hurt or dead. Reporter as the gunmen headed towards the stage they decided to make a break for it. When we found each other, there was another shooting. So we went back down on the floor. And then a few seconds after that, we heard a policeman near the entrance. And he said, come on, quick, go, hurry up, get out, get out we were climbing corpses climbing over corpses to get out . Yes, yes. Reporter they made it out but 89 died in that concert hall. Dozens wounded. A country left reeling. Minutes earlier gunmen in a black vehicle shot at people sitting outside the terrace of a restaurant. Roman lives in the neighborhood which he now calls a cemetery. I can tell you a picture that is still engraved in my mind, probably forever. The terrace of the restaurant with all the dead corpses that remained there for hours. Untouched. No cover, no blanket, nothing. And they were all dead. Almost in the position they were when they were having their drinks. Reporter roman did all he could to help. I just stayed beside her because her feet, she had no more shoes. I grabbed a survival blanket and put it back on her feet so she was not cold. She was dying. Reporter 19 people died. Nine were injured. Can you describe the sound of the shots . Its like heavy rain on a metal roof. Something like that. That fast . Really, really, really fast. Like really being exterminated. No feelings. No mercy. Nothing. Its not human, these people are not human. Reporter small wonder parisians are still jittery tonight. Yesterday pariss place de republique empty as if someone had pulled a plug. We saw panic from our hotel. Everybodys running. Reporter running for their lives, crouching under restaurant tables, doing anything to protect themselves. Police taking positions, aiming their rifles. It turned out to simply be fireworks. But for those who were actually in the crosshairs, the bigger questions like, will there be more attacks . Will it spread to the u. S. . Those will come later. In a way you feel so lucky to be alive. Because we dont know how we managed to do this. Reporter for nightline, matt gutman in paris. When we come back, stirring symbols of solidarity from every corner of the globe. Messages of peace for a world in mourning. Welcome to the most social car weve ever designed. The 2015 nissan murano. Recipient of autopacifics bestinclass Vehicle Satisfaction award. Now get great deals on the nissan murano. Its here, the first gummy multivitamin. From centrum. A complete, and tasty way to support. Your energy. Immunity. And metabolism like never before. Centrum multigummies. Imagine. One mans musical message and symbols of peace. The true colors of hope echoing around the globe in a tribute to paris. Amidst the horror and grief, a moment of hope. Davide martello outside the bataclan theater playing john lennons imagine. Music goes directly into your heart. You have a mirror in front of you nd youre reflecting yourself in this music. Reporter after those nowinfamous attacks the 34yearold musician drove 400 miles from germany to may at nearly every site where innocents lost their lives. My hope is that all the musicians all around the world are playing music for peace. Right now. Echoes of support. Monuments awash in the colors of the flag. This image trending worldwide. And in paris tonight, a symbol of hope in a city tossed but not sunk. Our thoughts once again but france tonight. 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