Highland Park Mayor Nancy Rotering told NBC's Today that the gunman who killed seven people and wounded 38 others during a Fourth of July parade obtained the gun legally.
"I don't know where the gun came from, but I do know that it was legally obtained," Rotering said.
Officials have not released the make of the gun or where it was purchased. The high-powered rifle was found on the roof of the building where the shooter, Robert "Bobby" Crimo, allegedly opened fire on a crowd of people attending the parade.
Rotering said that she has known the 22-year-old shooter for years and noted he was not on law enforcement's radar before the massacre.
"I know him as somebody who was a Cub Scout when I was the Cub Scout leader," she said. "It's one of those things where you step back, and you say, 'What happened? How did somebody become this angry? This hateful?' To then take it out on innocent people who literally were having a family day out."
Crimo was taken into custody following a brief chase with the police. Investigators have not determined a motive for the attack, and it is unclear what charges Crimo is facing.