Still pictures from the surveillance video show the crowd dispersing and some people falling to the ground. Then, a man in a white T-shirt and dark pants is seen running away.
Three people remain in critical condition. Authorities said most of the injuries weren't life-threatening. Ten men, seven women and a boy and girl, both 10, were hit by the bullets. The children only suffered graze wounds.
One witness, a medical student, said the gunman appeared to be firing in a controlled manner, but it wasn't clear if anyone in particular was targeted.
Police believe more than one gun was fired during the parade, and they have vowed to make swift arrests.
Police hope someone will recognize the man seen in the surveillance footage. A $10,000 reward is being offered for information leading to arrests and indictments in the case.
The Associated Press contributed to this report.