Witnesses reported panic and screaming after gunfire erupted during the Highland Park, Ill., Independence Day parade Monday, killing at least six people and injuring dozens.
Larry Bloom, who was at the parade when shots began, said at first spectators thought the "popping" sound was part of the parade.
"You heard like a 'pop, pop, pop,' and I think everybody kind of thought maybe it was a display on one of the floats and then it just opened up," Bloom said.
That thought quickly changed.
"I was screaming and people were screaming," Bloom said. "They were panicking and they were just scattering and I, you know, we didn't know. You know, it was right on top of us."
Gabriella Martinez said many thought the gunshots were fireworks, but things quickly changed.
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"We started hearing what we thought were fireworks in the beginning because we thought it would... I thought it was part of the parade so I told her like 'fireworks,' and then literally like one second (later) we all started getting into a panic mode," Martinez told NBC Chicago.
She noted that she saw a gunman on the rooftop of a nearby business aiming in her direction and ran with her daughter into another business on the street.
"I ran into the store and then we started running away from the doors and then like five minutes later I started like getting like into the reality that we were getting shot at like I was like in total shock mode," she said.
Dr. David Baum, who was at the parade and helped treat people injured in the shooting, said he saw several people shot.
"The bodies that I saw, it was not an image that anyone who's not a physician would have an easy time processing," Baum said.
A person of interest in the shooting was apprehended late Monday.
The shooting happened just after 10 a.m. near Central Avenue and 2nd Street in downtown Highland Park, according to reports. A large police presence from the state and neighboring suburban Chicago departments was seen along the parade route.
Streets were cleared along the parade route, as well as in nearby Glencoe, according to local reports.