Six people were killed and more than two dozen others wounded when a gunman started firing a high-powered rifle from a rooftop 10 minutes after the Highland Park Fourth of July parade kicked off Monday morning, authorities said.

Authorities continued to hunt Monday afternoon for the shooter, and “the offender still has not been apprehended so far,” Christopher Covelli of the Lake County sheriff’s office and the Lake County major crimes task force said at a news conference around 2:15 p.m., four hours after the shooting.

The gunman used “a high-powered rifle,” Covelli said and fired from a rooftop. “He was very discreet and very difficult to see.”