Transcript for 2 Americans among 8 killed in NYC truck attack
They're stuck in here! Reporter: You can hear the Panik their voices. Are you okay? Oh my god. Reporter: This man getting his first look at the mangled school bus -- Did you call 911? Oh my god, oh my god. The guy t-boned -- come on there's kids right there. Reporter: Police and fire crews rushing in to save the children. Oh my god. Reporter: This moment captured minutes after the suspect, sayfullo saipov, allegedly took a rental truck on a path of terror. This was an attack on united States of America, an attack on New York City, an attack on our people, and it was the definition of terrorism. Reporter: Tonight we're being told that he planned this for weeks. Even making a dry run. And that he's now bragging from his hospital bed, proud of what he's done, declaring he was inspired by ISIS. The other items recovered at the scene was some notes, the gist of the note was that the islamic state would endure forever. Reporter: He killed eight people on his rampage and injured a dozen more. There are families today feeling pain that is unimaginable. Reporter: Most of the victims came from this group of friends visiting the city from Argentina. This video captured what started as a fun day here in New York City to celebrate the 30th anniversary of their high school graduation. But it ended in horror. Five members of the group dead. Ann was a 32-year-old mother of two visiting from Belgium. Two of the victims were American. I'm not angry at all. Reporter: Jimmy drake simply cannot quite believe that his only child is gone. It was one of those father-son relationships -- Reporter: Darren drake, 32-year-old project manager on a bike ride between work meetings when he was run down. He was born three blocks away from where we just identified the body. Reporter: Also killed, 23-year-old Nicholas cleeves, also an only child. He lived with his mother a few blocks from the scene. I love him so much. I consider him my friend. Our hearts break for them and we pledge to renew our resolve in their memory. Reporter: Investigators say the suspect, sayfullo saipov, chose Halloween because he knew the streets and sidewalks would be crowded. Police say just after 2:00 yesterday, saipov rented the truck at a Home Depot in passaic, New Jersey. 2:43, the license plate readers on the George Washington bridge show him exiting the bridge into New York City. 20 minutes later a port authority camera outside the Holland tunnel shows the truck driving into the bike lane, going fast. Be advised, we have multiple people on the ground from chambers all the way up to Houston -- Reporter: The rampage ended when the truck smashed into that school bus, which was carrying children. You can see saipov running through traffic, appearing to ho what looked like two guns in his hands. NYPD officer Ryan Nash and his partner responded, quickly confronting saipov. Nash shot him in the abdomen. The officer, just 28, now hailed as a hero. He thinks what he did was not an act of heroism, he thinks it's something that -- why he joined the police department. Although I feel we were just doing our job, like thousands of officers do every day, I'm grateful for the recognition we have received. Reporter: This video shows the immediate aftermath of the attack, dead and injured lying in the bike path. The injuries ranged from a bilateral amputation to serious head, neck, back, and chest trauma and trauma to arms and legs. Reporter: 12 people rushed to local hospitals. Many of them still in treatment tonight. Investigators say the weapon saipov was holding included a paint ball gun and pellet gun and three knifes. He was wheeled into court earlier today where he was formally charged. Just about 24 hours after saipov's attack, we now have him charged with federal crimes of terrorism. A federal charge of violence and destruction of a motor vehicle with willful disregard for the safety of human life that resulted in multiple deaths. Reporter: Investigators swarmed his home in Paterson, New Jersey. The 29-year-old lived in this apartment with his wife and three children. Officials confirm saipov moved to the United States in 2010, passing all the necessarily checks. He was part of a diversity Visa lottery, a program that allows for immigration from countries that have low immigration rates to the U.S. Today president trump used the attack to bolster his argument for a change in immigration policy. I am today starting the process of terminating the diversity lottery program. Sounds nice, it's not nice. It's not good. Reporter: The president also had strong words for the attacker. We also have to come up with punishment that's far quicker and far greater than the punishment these animals are getting right now. Reporter: But it was the difference in that response and trump's response to the massacre in Las Vegas that caught the attention of some. After the horrific shooting in Las Vegas, the president repeatedly said, now is not the time to talk about policy, now is not the time to talk about politics. Why was he so quick to go the political route -- Look, this wasn't about going the political route, this is something frankly the president's been talking about for a long time. This isn't a new policy. This isn't a new position. This isn't a new conversation. You had an episode of an immigrant who happened to be Muslim who was attacking Americans in the name of Islam. That is terrorism and it's exactly the kind of terrorism that president trump views as a threat. He doesn't view and hasn't viewed the same kind of threat of gun violence as exhibited in Las Vegas, for instance, as he does around this. And he tapped into the fears of a lot of Americans during his campaign around just these sorts of episodes. Reporter: As it happens, Uzbekistan, where the suspect was born, is not among the countries listed on the president's travel ban. But there have been recent terror ties to the country. He was the point of contact, the primary point of contact, for, and this is preliminarily, 23 people that came in or potentially came in with him. Reporter: U.S. Officials tell ABC news at least two of those 23 were suspected of possible links to terror. He was considered the point of contact for those 23 people. They may have been friends, relatives. Two of them, we're told, were people that had suspected ties to terrorism. Reporter: Tonight we're lea learning much more about the suspect, saipov, and what inspired him. A man consumed by hate and a twisted ideology. Reporter: Law enforcement says saipov told them he decided to carry out the attack a year ago. Authorities also recovered two cell phones from the scene. Revealed thousands of isis-related images and 90 videos, about 90 videos, depicting, among other things, ISIS fighters killing prisoners. Reporter: And authorities say he made this chilling request. Saipov asking whether he could fly the ISIS flag in his hospital room. It's been my experience in interviewing other high-profile terrorists that they want to talk to you, because they're proud what was they've done. Reporter: According to investigators, had he not hit that school bus, he would have continued down a highway and onto the heavily trafficked Brooklyn bridge. Tonight, of course, the burning question, how did a man with a wife and three children, who has jobs driving for both Uber and Lyft, become radicalized? Most people in the U.S. Get radicalized through the internet. Because we don't have face-to-face, on-the-ground recruiters for groups like ISIS. Reporter: Dr. Beck hart, research psychologist and security expert focused on violent extremism. ISIS is willing to use anyone. They're looking for people with access, particularly weapons trained, so they would love to get somebody from the military or the police. But they're willing to use mentally ill people that feel discriminated against or alienated. Reporter: For the past few years: Speckard has interviewed dozens of ISIS defectors and their family members, and she says she worries there aren't preventative systems in place here in America to report people showing signs of radicalization. We need hotlines that family members can call and ask advice and ask how they can intervene. And that we need rapid intervention teams that deploy immediately with a counselor and an Imam so that they can say, no, no you've got Islam all wrong, this is not what Islam says and you will not an martyr and you will not go immediately to paradise for killing innocent civilians. Reporter: Tonight New York City is on high alert with a major public event looming, the New York City marathon, this weekend. 2.5 million spectators will line the streets. We've added more trucks more locker vehicles, more than doubled observation teams, rooftop observation posts, as well as counter-sniper teams. Reporter: New York City is no stranger to terrorism, and in its darkest hours we often see a spirit of unity and strength shining through. Be strong, be proud, be resilient. Show the whole world right now that we will not be moved by terror. Tune in to "20/20" on Friday for the Diane sawyer special "ISIS in America."
This transcript has been automatically generated and may not be 100% accurate.