A colourful Independence Day parade in highbrow Highland Park turned bloody when a gunman perched on a rooftop opened fire on families waving flags and children riding bicycles on the parade ground.
At least six people were killed while about 36 others were wounded.
Highland Park is a community of about 30,000 residents some 40km (25 miles) north of Chicago, Illinois.
Clips emerging from the scene (see our Telegram Channel) show the moment the shooter opened fire, with seated families momentarily taken aback and thinking it is gun salute or fireworks meant to be part of the celebration.
The moment it dawns on them what is happening, the attendees spring to their feet and flee in various directions.
A father pushing a special need son on a wheelchair struggles to get the son and himself out of the danger and wheelchair tumbles in the process.
Mothers with strollers push their kids frantically as they all struggle to get out of danger.
A “person of interest” in the shooting, identified as 22-year-old Robert E Crimo III has been arrested. (See picture above).
According to Highland Park Police Chief Lou Jogmen, a police officer pulled over Crimo III about 8km (five miles) north of the shooting scene, several hours after police released the man’s photo and an image of his silver Honda Fit, and warned the public that he was likely armed and dangerous.
His motive is not yet known.
A spokesperson for the Lake County Major Crime Task Force, Christopher Covelli, told reporters the attacker apparently used a “high-powered rifle” to fire from a spot atop a building where he was “very difficult to see”.
“Very random, very intentional and a very sad day,” he said.
“Our community was terrorised by an act of violence that has shaken us to our core. Our hearts go out to the families of the victims during this devastating time,” Mayor Nancy Rotering told reporters on Monday afternoon.
The Chicago Sun-Times newspaper reported that the parade began about 10 am local time (15:00 GMT) but was suddenly halted 10 minutes later after shots were fired.
An attendee, Amarani Garcia, who was with her young daughter, told the local ABC affiliate she heard gunfire nearby, then a pause for what she suspected was reloading, and then more shots again.
There were “people screaming and running. It was just really traumatising”, Garcia said. “I was very terrified. I hid with my daughter actually in a little store. It just makes me feel like we’re not safe anymore.”
Nicolas Toledo, a man in his late 70s, was the first victim identified as of late Monday by his family. He was in a wheelchair and had not wanted to attend the parade, his family said in a statement to local media. But he required full-time care and his family said they had not wanted to miss the event.
“My grandfather Nicolas Toledo father of 8 and grandfather to many left us this morning July 4th, what was supposed to be a fun family day turned into a horrific nightmare for us all,” his granddaughter Xochil Toledo said in a statement shared by the family on social media.
“As a family we are broken, and numb,” she added.
See footage of the onset of the shooting on our Telegram channel here.