The shootings took place near the city’s main Jewish synagogue, the 19th-century Stadttempel. The temple was closed at the time, and it was not clear if it had been a target, but it was the scene of a terrorist attack in 1981 that killed two people and left dozens wounded.
Video broadcast on local media Monday showed an assailant wearing a black hood running up to a man, shooting him at close range with a long gun, running away and then returning seconds later to shoot him twice more with a handgun. A spokesman for the Interior Ministry, Harald Sörös, described the victim as a passer-by.
That video was one of several that made their way onto social media and local news broadcasts purporting to show snippets of the chaos and bloodshed. The authorities urged people to hand such video over to them, rather than posting them publicly.
One video showed people aiding a wounded person lying in a pool of blood, just outside a restaurant on Ruprechtsplatz and less than a mile from the Austrian Parliament building. Several chairs in the restaurant’s outdoor area had been overturned, as if abandoned in a hurry.
Another video showed a gunman firing a rifle twice down a street, though the target could not be seen, and in others, people ran for cover or ducked behind obstacles as shots echoed through the streets, and heavily armed police officers took up positions around the area.
“We just saw quite a few people running, had no clue what was going on, then heard the shooting and a few people screaming,” said Julia Schrammel, who was having dinner with her three cousins at Motton am Fluss, a restaurant on the riverfront, when the attack took place.
“It took them a while to lock down the restaurant, but now we are locked down here,” Ms. Schrammel, a 24-year-old student, said hours after the shooting began. “We are watching the news from a TV in the restaurant, there are all sorts of rumors going on.”