A gunman opened fire into a crowd that had gathered downtown for the city's annual fireworks display, injuring nine people and forcing hundreds of revelers to scatter.

Police Chief Ella Bully-Cummings said Wednesday night's shooting apparently followed an argument and that innocent people were caught in the crossfire.

Police questioned several people but had made no arrests, city spokesman James Tate said. He would not say whether police knew the shooter's identity or target.

"There were a lot of different accounts of what happened," Tate said.

Bully-Cummings said investigators recovered a handgun from the Hart Plaza (search) area and had a good description of the suspect. She said police got photographs of potential witnesses from a bystander's digital camera.

Nine people — four men and five women, ranging in age from 17 to 47 — were shot, police said. On Thursday afternoon, three were listed as "critical but alert," three were stable and three had been treated and released, a hospital spokeswoman said.

One victim, a 22-year-old man, suffered a bullet wound to his heart, police said.

Hundreds of thousands of people packed into downtown and along the Detroit River (search) that runs between Detroit and Windsor, Ontario, to watch the display, a summertime tradition that celebrates the bonds between the cities.