Highland Park shooting at July 4 parade in Illinois

Law enforcement search a building after a shooting at the Highland Park Independence Day parade in Illinois on July 4. (Nam Y. Huh/AP)

Sgt. Chris Covelli, from the Lake County Major Crime Task Force, said the investigation is still active and will continue to be active while law enforcement officers work to find the alleged shooter and uncover what happened.

“This is two-pronged at this time — number one, we are aggressively looking for the individual who’s responsible for this shooting. Number two, we have the criminal investigation that is occurring simultaneously,” he said.

“This is very active and it’s going to remain very active for the time to come,” Covelli added.

He said police are working with the FBI and there are more than 100 law enforcement officers on the scene. He urged people to look through their phones and see if they have any photos or videos from the time the shooting started. He said any material could help police.

“Please understand we can’t give away certain aspects of the investigation, we don’t want to negatively impact… We want to arrest the offender and hold him accountable for his actions,” Covelli said at a news conference on Monday.

Cmdr. Chris O’Neil, of the Highland Park Police, said the rifle that was found was discovered on a rooftop. Earlier Monday, officials said they could not disclose specifically where the rifle was found. Police say they believe the shooter appeared to fire shots from a rooftop.