Transcript for Canadian Parliament Shooting Launches New Terror Alerts
Terror in Canada's capital city today. Just across the border. A soldier gunned down in cold blood, shots ringing out in the parliament building. Putting the American embassy there on lockdown. Tonight, new information about the alleged killer, believed to be a Canadian jihadist with a police river for drug and robbery arrests. With 90 other radicals there possibly tied to islamic extremist groups, what's the threat here at home? My "Nightline" co-anchor Dan Harris is on the scene. Dan? Reporter: Juju, good evening to you from ottawa. We're standing now about a block away from where these sheetings were carried out earlier today. And just now, part of the grim choreography of these things. A makeshift memorial is starting to grow here right near the scene. All day long, we saw some shocking images. And we also heard about one extraordinary act of courage. Everybody out. Reporter: A day of mayhem and fear in the halls of Canada's parliament and on the streets of ottawa. Canada's capital city, just 60 miles from the American border, paralyzed. It all started before 10:00 A.M. At Canada's national war memorial. A man with a rifle shot and killed corporal Nathan Cirillo who was dressed in ceremonial uniform, guarding the tomb of the unknown soldier. Some bystanders rushing to his aid. Others in shock. Third, fourth shot. He took off. Yelled at guys, everyone, you know, get down, get down. Get out of the way! Reporter: Police, guns drawn, began hunting for the shooter. War memorial. Call for shots fired. We may have multiple patients. One soldier has been hit. Reporter: Just two minutes after the initial shooting, another attack. This time, inside the packed parliament building, just steps away from the war memorial. Reporter josh Wingrove holding onto his camera through all of it. We heard gunshots come up from there and sort of ducking my held down the hall, we saw the smoke from the guns, you could smell it almost instantly. Reporter: Members of parliament barricading doorways with chairs and tables. Two rapid fire bursts of gunfire were heard just outside our room. And at that point, we just barricaded the room. Reporter: Police swarming rooftops. Sweeping the government complex. Some workers huddling in the dark. Others scrambling to safety. Meanwhile, the prime minister, Stephen Harper, who was in the building at the time, was whisked away to an undisclosed location. The rampage in the parliament building, finally ended when sergeant at arms Kevin Vickers shot and killed the gunman. Lawmakers taking to Twitter to praise Vickers as a hero. As police tried to figure out how many gunmen were on the lose and in how many locations, such of the city went into lockdown, including the heavily fortified U.S. Embassy. For hours, people were ordered off the streets and away from windows, as officers swarmed the city center. Everyone needs to leave now! Leave! Reporter: They went building to building, clearing shops and ushering people to safety. Come on out. Straight down along the souide of the building. This is an ongoing operation. We are asking members of the public to stay away from the downtown core. Reporter: The lockdown still in place when we arrived in ottawa in the late afternoon. You can tell we're in an area that is going through an emergency. We're seeing ambulances, paramedics and just police all over the place. Most of the street's blocked off. It's going to be hard for us to get close to the scene at this point. And then, shortly after president Obama weighed in from Washington, D.C. -- We don't yet have all the information about what motivated the shooting. Reporter: A major development. We learned the name of the suspected shooter. Canadian Michael see half by bow. Sources telling ABC news he was 342 years old, born in Canada and a recent convert to Islam. Investigators in Canada and America immediately began hunting for clues on the suspect. Today's attack came at a time of heightened alert here in Canada. Just two days ago a man who had been on a terror watch list here and who had boasted of his ties to Isis targeted two Canadian soldiers in Quebec after laying in wait for two hours, he used his car to run the soldiers down, killing one of them and wounding the other. He was shot and killed after flipping his vehicle during a high speed chase and this knife was recovered at the scene. What took place yesterday is clearly linked to terrorist ideology. Involved in the investigation in the June 2014. Reporter: The man who was described by local officials as ral cadized has been arrested why trying to leave the country. We could not have enough evidence to charge him and to detain him, so we released him. Reporter: Radicalization is a growing problem here. Authorities say so many Canadians have gone to Syria to join Isis that they've ooichb created their own recruitment videos with iconic Canadian scenes. Before Islam, I was like any other regular Canadian. I watched hockey. Reporter: Canadians have been seen burning their passports and carrying out brutal murders. An the internet has been brimming with Isis propaganda videos, with calls to kill Canadians along with other allies of the U.S., using whatever weapons are available. The dangerous part of this is, when you see one attack, it tends to crop up others. I would not be surprised at all if there are more in Canada and across the west in general. Reporter: Late in the day here in ottawa, one bit of good news. The three people sent to the hospital during the attack were discharged. For the second time this week, there has been a brutal and violent attack on our soil. Reporter: Late tonight, the prime minister addressed the nation, vowing not to be intimidated, but not answering many of the pressing questions. Such as, what was the motive? And did he act alone? We will learn more about the terrorist and any accomplices he may have had. Reporter: These are pressing questions for America, too. The violence here in Canada raising new and troubling concerns about the security of our 4,000-mile border to the north. The largest unmilitarized border on Earth. As we come on the air tonight, the area under parliament here in ottawa is still off-limits as police conduct what they call an active and dynamic investigation. And this country, so new to this kind of violence, is dealing with shock, uncertainty and some serious soul-searching to come. For "Nightline," this is Dan Harris in ottawa, Canada.
This transcript has been automatically generated and may not be 100% accurate.