HIGHLAND PARK, Ill. — It sounded at first like fireworks to the parents who had brought excited children to a charming Fourth of July parade in their town. Or perhaps a military salute to the flag.
But within seconds, as marching band members and politicians strutted down the street, horrified spectators realized the noise from a nearby rooftop was a high-powered rifle spraying bullets into the crowd, killing six people and wounding dozens.
The attack in Highland Park, a usually safe lakefront suburb north of Chicago, set police on a sprawling manhunt that forced residents to shelter in place for much of the day, and prompted neighboring cities to cancel their holiday events. About eight hours later, the police said they had taken into custody a 22-year-old man whom they described as a person of interest.
Even in a country battered from the constancy of mass violence — at grocery stores and elementary schools and on urban street corners — the carnage in Illinois proved shocking. According to the Gun Violence Archive, a nonprofit research group, the shooting on Monday was the 15th this year in which at least four people were fatally shot in the United States.
For reasons that remained unclear to the police Monday evening, officials said a young man had climbed onto a rooftop with a rifle and begun firing into a sea of families in lawn chairs who were celebrating Independence Day.
“My wife looks up and screams, ‘Get up, run. Get up, run,’” said Shawn Cotreau, 47, a Massachusetts resident who was visiting family in Illinois, and who said he initially thought there were firecrackers nearby.
Mr. Cotreau estimated his family was sitting in chairs about 20 feet away from the gunman, who was on the roof of a store firing down.
“I can’t even get the image of the guy out of my head,” he said, describing a man with a large gun, wearing fatigues and a hat pulled down. “He was just opening up fire. And I saw the bullets hitting the tree that was like literally in front of us.”
Police officers, who were already assigned to the parade route, arrived and rushed to help the wounded, the authorities said. Victims ranged in age from 8 to 85, doctors who received the injured at local hospitals said.
The gunfire stopped around the time officers arrived, police said, and the gunman was able to get away. By late afternoon, SWAT teams were still combing the area, and officials were asking residents and businesses to turn over photos or videos that might provide clues. Authorities warned that he was believed to be armed, and told the public not to approach him.
“Could this happen again?” Deputy Chief Christopher Covelli of the Lake County Sheriff’s Office asked Monday afternoon, while the search for a gunman was on, and as other Chicago suburbs rushed to cancel parades and fireworks shows. “We don’t know what his intentions are at this point.”
Robert E. Crimo III was taken into custody in nearby Lake Forest after a brief chase, the police said.
Survivors described a joyous family event, with high school football players and a marching band that turned suddenly into a scramble to live. Dr. David Baum, an obstetrician who had come to the parade to watch his 2-year-old grandson push a bubble lawn mower alongside dozens of other children, said he rushed to help after what sounded like a sonic boom and people yelling, “‘Bodies down, bodies down!’”
Diego Rosas, who was working at a grocery store near the parade route, heard perhaps 30 shots, then saw people running toward the store. He let them inside.
Alexander Sandoval, who had arrived early with his family long before the parade started to stake out a prime viewing spot, said he did not immediately realize what was going on.
“When it started happening, I thought it was the Navy saluting the flag,” said Mr. Sandoval, a construction contractor and a lifelong resident of Highland Park. “Then I grabbed my kid and we ran and tried to break a store window to get away from it.”
Mr. Sandoval said he also tried to break a door down at a closed business, but then had to continue running.“I was punching the door but couldn’t punch through it,” he said. “I think the shooter stopped and reloaded, and that’s when I ran around the corner and put my son and little brother in a dumpster.”
Mr. Sandoval said he saw a police officer carrying a wounded boy about the age of his own child. “It’s just emotional,” he said.
The shooting brought outpourings of sympathy from across the state and country, and renewed pleas among Democrats for stricter gun laws, barely a week after President Biden signed the most significant gun legislation to clear Congress in decades. President Biden said he was “shocked by the senseless gun violence.” Gov. J.B. Pritzker of Illinois, a Democrat, vowed to “end this plague.”
“There are no words for the kind of monster who lies in wait and fires into a crowd of families with children celebrating a holiday with their community,” the governor said. “There are no words for the kind of evil that robs our neighbors of their hopes, their dreams, their futures.”
Those victims included Nicolas Toledo, who had recently moved back to Highland Park from Mexico to spend more time with his family, according to his granddaughter, Xochil Toledo.
Ms. Toledo said her family had gone out at midnight to line up chairs so 15 of them could be together for the Fourth of July. Three in that group would be shot.
“We brought him over here so he could have a better life,” Ms. Toledo said of her grandfather. “His sons wanted to take care of him and be more in his life, and then this tragedy happened.”
After the shooting, 26 people were taken to Highland Park Hospital, 25 of them with gunshot wounds, said Dr. Brigham R. Temple, the medical director for emergency preparedness at NorthShore University HealthSystem. At least 10 other patients were taken to nearby hospitals, he said. Their injuries ranged from minor to severe.
With downtown still considered an active crime scene and residents encouraged to stay inside, many in Highland Park spoke of a mix of shock, grief and anger.
“On a day that we came together to celebrate community and freedom, we’re instead mourning the loss, the tragic loss, of life and struggling with the terror that was brought upon us,” Mayor Nancy Rotering said.
“I think every parent now in this community and every other community starts to look at risk completely differently,” said Dr. Baum, before referring to the mass shooting in Uvalde, Texas, that left 19 children and two teachers at an elementary school dead. “Uvalde is a couple thousand miles away, but Uvalde happened in Highland Park in a different way.”
The attack on Monday came less than eight months after the driver of an S.U.V. stormed through a Christmas parade in Waukesha, Wis., about 80 miles northwest of Highland Park, killing six people and wounding dozens more.
In Illinois, Chief Covellisaid that officials had recovered a rifle, and that hundreds of local, state and federal law enforcement officers had searched for the gunman.
The Lake County coroner said at least five of the six people who died were adults. Officials did not immediately release their names.
News of the shooting rattled people across the Chicago area, as officials weighed whether to go forward with their own celebrations amid the grief and the manhunt.
Several cities and towns called off parades and fireworks displays, and even closed beaches. In Highland Park and neighboring Deerfield, residents were advised to stay indoors.
Michelle Bernstein, a resident of Deerfield, said the her two teenage daughters were at friends’ houses at the time of the shooting. She told them to stay there until the gunman was apprehended. One of her daughters was scheduled to work as a lifeguard at a local pool, she said, but the pool closed for the day.
“I’m hoping they catch the person so my kids can come home,” Ms. Bernstein said in the hours before a person of interest was taken into custody. “Right now I don’t want to go outside.”
And as the afternoon dragged on without an arrest, signs of sudden terror remained scattered along the parade route.
Abandoned strollers and empty lawn chairs, some with half-consumed drinks in the cupholders, were lined up along the sidewalk. A child’s bicycle was discarded along the curb. And a cheerful-looking balloon, left alone in the grass, said “God bless America.”
Maggie Astor, Adam Goldman, Michael Levenson, Noam Scheiber and Alan Yuhas contributed reporting.