HIGHLAND PARK, Ill. (WLS) -- Six people were killed and 31 injured in a shooting at the Highland Park 4th of July parade Monday.
Law enforcement said the shooting appeared to be random. Robert "Bobby" E. Crimo, III was identified as a person of interest in the shooting, and was taken into custody at about 6:30 p.m.
Police said a North Chicago police officer spotted Crimo at Route 41 and Buckley Road. There was a brief pursuit, but the vehicle was stopped at Westleigh Road and 41 in Lake Forest.
Crimo was taken into custody without incident. He will be taken to the Highland Park Police Department for questioning.
Crimo has ties to Rockford, DeKalb and Elgin, police said.
Law enforcement sources confirmed to ABC News that Crimo's social media posts are part of the ongoing investigation. One video shows cartoon characters being shot, according to ABC News.
Police said the shooter used a high-powered rifle from atop a high building.
VIDEO: People flee as shots fired at Highland Park parade
The parade was stopped about 10 minutes after it kicked off at 10 a.m. when shots were fired, sending hundreds of people running for safety.
The parade route was near Central Avenue and Second Street.
Several witnesses said they heard multiple shots fired. One witness said he counted more than 20 shots.
WATCH: Suburban parade shooting witnesses describe fleeing from gunfire, hiding children
"I thought it was the navy saluting the flag with rifles but then I saw people running, I picked up my son and started running. I ran to one of the buildings, I tried to break glass into get in with my son and I couldn't break it," said Alexander, a witness. "It was horrible. When I went back there were a few people shot on the ground... There was no target... it was shooting whoever."
A gun was recovered at the scene, and the Bureau of Alcohol, Tobacco, Firearms and Explosives is urgent tracing it to find the original purchaser of the firearm. The ATF told the ABC7 Chicago I-Team "that will tell us a lot" about "where and when it was purchased and by whom."
Those in the area were urged to stay inside and remain alert and calm. Some mandatory evacuations were taking place.
"You're not safe anymore, you're not going wanna take your kids to a large gathering. And you're always going to have that. Like when you get a in a car accident, traumatic," Alexander said.
WATCH: Highland Park shooting witness captures gunshots on video
A family reunification center was established at the Highland Park police station, located at 1677 Old Deerfield Road.
Anyone with video of the incident is asked to call police.
WATCH | 'Bodies were blown up by AR-15s': Dr. David Baum describes parade shooting
A crime scene was established throughout the central business district, and a perimeter set up from Green Bay Road to Laurel Avenue to St. Johns Avenue to Elm Place.
There was a heavy police presence near McDaniels Avenue and Deerfield Road, as well.
Some of the injured were taken to Highland Park hospital for treatment, where they were in serious-to-critical condition, a Lake County Sheriff's Office spokesman said.
The vast majority suffered gunshot wounds, and the remaining suffered injuries as a result of the "ensuing chaos," hospital officials said.
Five adults died on the scene, and one person died in a hospital, the Lake County Coroner's Office said. At least one child was among those injured.
Highland Park hospital staff said they received patients ranging in age from 8 to 85.
Police were telling people, "Everybody disperse, please. It is not safe to be here."
WATCH: Video shows people fleeing gunfire at Highland Park parade
Bystanders were quick to tie tourniquets, which helped paramedics.
As they fled the parade route, parade-goers left behind chairs, baby strollers and blankets as they sought cover, not knowing just what happened.
One witness said "it looked like a war zone," and he was almost trampled in the stampede after the shots were fired.
"This should not happen in our country," Paul Chesler said.
WATCH: Witness describes Highland Park shooting as 'war zone'
"All I thought about was getting my daughter to safety, I ran with her, we went to the nearest McDonalds and she lost her shoe along the way, she was scared, all I just wanted was her to be safe," said Armani Garcia. "She was in front of walker brothers, she was gonna come sit next to us. I'll have the girls cross over. They never made it across. The parade was going on and that's when everything happened."
For three hours, Donald Johnson hid in a gas station.
"There were six or seven children crying their eyes out, and the mothers finally got them settled down by singing 'The Wheels On The Bus Go Round and Round,'" he said.
State Sen. Julie Morrison said she was about a block away from the shooting.
"We heard gunshots that I kind of thought it was fireworks, then all of a sudden this wave of people starts running back towards us screaming, crying, hysterical, carrying their kids," Morrison said.
In the aftermath of the shooting, police patrolled the area with rifles.
U.S. Rep. Brad Schneider said he and his campaign team were gathering at the start of the parade when the shooting began.
"My team and I are safe and secure," he said. "Hearing of loss of life and others injured. My condolences to the family and loved ones; my prayers for the injured and for my community; and my commitment to do everything I can to make our children, our towns, our nation safer. Enough is enough!"
A woman who was at the parade with her family said her best friend's sister was among those shot.
"People screaming and running, it was just really traumatizing and scary," she said. "All I thought about was getting my daughter to safety. I ran with her. We went to the nearest McDonalds. She lost her shoe along the way, my daughter. She was scared. All I want is her to be safe."
Ariel Rotbol was walking in the parade with a state representative when she heard the gunshots.
"It was a war scene," Rotbol said. "People just in hysteria. We saw the helicopter, the cars, Homeland Security coming in. In Highland Park, we have not experienced this yet and I don't think anybody obviously thought this is what was going to happen today and it is just hard to fathom."
Lake Shore Country Club was also locked down.
The city of Highland Park said the city's Fourth Fest had been canceled.
President Joe Biden released a statement on the incident, saying, "Jill and I are shocked by the senseless gun violence that has yet again brought grief to an American community on this Independence Day. As always, we are grateful for the first responders and law enforcement on the scene. I have spoken to Governor Pritzker and Mayor Rotering, and have offered the full support of the Federal government to their communities. I also surged Federal law enforcement to assist in the urgent search for the shooter, who remains at large at this time. Members of the community should follow guidance from leadership on the ground, and I will monitor closely as we learn more about those whose lives have been lost and pray for those who are in the hospital with grievous injuries.
"I recently signed the first major bipartisan gun reform legislation in almost thirty years into law, which includes actions that will save lives. But there is much more work to do, and I'm not going to give up fighting the epidemic of gun violence."
Deerfield's Family Days at Jewett Park was canceled.
Evanston canceled its parade and fireworks and closed its beaches after the incident.
WATCH: State Sen. Julie Morrison describes shooting scene
"Out of an abundance of caution, today's Skokie Fourth of July Parade has been canceled due to the shooting incident at the Highland Park Fourth of July Parade. The Skokie community grieves with our neighbors in Highland Park," Skokie officials said. "A decision will be made later today regarding tonight's fireworks at Niles West High School."
Gov. JB Pritzker tweeted, "My staff and I are closely monitoring the situation in Highland Park. State police are on the scene and we have made all state resources available to the community. We will continue working with local officials to help those affected."
In a full statement, he said:
"Today, I ask all Illinoisans to pray for the families who have been devastated by the evil unleashed this morning in Highland Park, for those who have lost loved ones and for those who have been injured. I also ask that we all pray for our first responders at all levels of government who are actively working to bring the suspect into custody, and whose bravery undoubtedly saved innocent lives on the scene."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. There are no words for the kind of evil that robs our neighbors of their hopes, their dreams, their futures. There are no words I can offer to lift the pain of those they leave behind. Please know that our state grieves with you, that MK and I grieve with you."But grief will not bring the victims back, and prayers alone will not put a stop to the terror of rampant gun violence in our country."I will stand firm with Illinoisans and Americans: we must - and we will - end this plague of gun violence."
During a press conference later, he added, "it is devastating that a celebration of America was ripped apart by our uniquely American plague."
WATCH: Witnesses describe scene of deadly shooting
Chicago Mayor Lori Lightfoot released the following statement on the shooting:
"Thanks to the heroic efforts of law enforcement, a person of interest in the horrific Highland Park mass shooting is in custody. I hope this provides a bit of solace to those who are deeply grieving tonight in the wake of today's unspeakable tragedy. My heart aches for the people of Highland Park. We must continue to lift up this community, the victims, and their families in prayer. Gun violence does not respect geographic boundaries or socioeconomic differences. It is a plague that affects us all. Whether it is Back of the Yards, Englewood, West Garfield Park, Uvalde, Buffalo, or now Highland Park, none of us are immune, and all are vulnerable without a federal effort to take weapons of war out of the hands of civilians. It can be done, it must be done, and we must continue to move toward that goal with all deliberate speed. We cannot be truly free unless we are relentlessly brave."
Morton Grove also canceled its parade.
"All remaining Northbrook 4th of July activities, including the bike parade, mile-long parade, and fireworks show have been canceled following the news of a shooting in Highland Park earlier today. Our thoughts are with our Highland Park neighbors," the village said.
Mayor Lori Lightfoot released a statement, saying, "The tragedy unfolding in Highland Park is devastating. I have been in contact with Mayor Rotering and have offered our support, and the Chicago Police Department is providing assistance. We grieve with the families of the deceased and injured as well as the entire Highland Park community. Law enforcement is working hard to bring the shooter into custody. If anyone has information, we encourage them to call 911 and report what you know."
Lake Forest is cancelling the Annual Lake Forest Festival and Fireworks planned at Deerpath Community Park out of an abundance of caution.
"The City extends its deepest condolences to our neighbors in Highland Park," Lake Forest officials said.
Waukegan canceled its fireworks Monday.
Elected officials react to deadly Highland Park parade shooting
"The City of Waukegan has canceled this evening's fireworks due to the tragic events in Highland Park. We stand in solidarity with our neighbors in City of Highland Park, Illinois," Waukegan officials said.
The Chicago Office of Emergency Management and Communications also released a statement on the incident.
"The Chicago Office of Emergency Management and Communications (OEMC) and the Chicago Police Department (CPD) are monitoring the incident that has taken place in Highland Park. While there are no known threats to Chicago at this time, we continue to maintain situational awareness of activity and events taking place throughout the City of Chicago. As a precautionary measure, we will have infrastructure assets staged at predetermined locations. Our thoughts are with the families of the deceased and injured as well as with the entire Highland Park Community," OEMC said.
Arlington Heights officials said the remaining scheduled activities at Frontier Days, including the evening concert, have been canceled.
Mount Prospect canceled its Fourth of July parade, the remainder of the Lions Club Festival at Melas Park and the fireworks display Monday evening.
WATCH: Rep. Brad Schneider speaks on Highland Park parade shooting
"Our hearts are with the Highland Park community after the tragedy that occurred this morning," local officials said.
Cook County Board President Toni Preckwinkle released a statement, saying,
"Cook County stands with Lake County and the Highland Park community following the tragic mass shooting that occurred during their 4th of July parade earlier today. While the situation remains fluid, we are standing by to support law enforcement and our neighbors to the north in any way we can. We will continue to monitor the situation and extend our resources and overall support to the people of Highland Park."We must, we all must, focus on stemming the flow of illegal guns and implementing common sense gun laws."My continued thoughts are with the families and loved ones who have lost someone and for everyone struggling to comprehend today's latest senseless act of gun violence."
Buffalo Grove canceled its Fourth of July events, including the Symphonic Band concert and fireworks display.
The North Shore Congregation Israel released the following statement after the shooting:
"We are horrified by the sickening and senseless shooting today at the Highland Park July 4th Parade. Our hearts break for those who have been murdered and wounded, along with all of their loved ones. Our thoughts and prayers are with our entire community, our neighbors and friends, and all of the first responders and police on the scene. We join with all people of good will in our heartbreak that such senseless violence and loss of innocent human life have once again wreaked havoc, this time in the midst of our own community, neighborhood, congregation and home. This touches each of us deeply and personally; the grief, pain, and fear affect us all.We remain in close contact with law enforcement as well as our own crisis team. Once the shooter is apprehended, we will plan to convene communally to pray for healing and solace. We will email with details once available and post here on our website. In the meantime, your clergy team is here to be of support. If you would like to talk, please email Rabbi Geffen, Rabbi Greene or Cantor Goldstein and one of us will get back to you as soon as we are able.We pray that the memories of the victims be for a blessing; we pray that their loved ones somehow find comfort amidst such destruction, that the pain of suffering be eased; we pray that the wounded find healing, that justice be swift, and that there might one day be a world of shalom, peace."
Libertyville and Itasca have canceled their fireworks for Monday night.
Elk Grove Village canceled its concert and fireworks.
WATCH: Residents speak outside Highland Park reunification center
Rolling Meadows canceled its fireworks.
Glenview canceled its parade and fireworks.
Winnetka canceled its fireworks show.
Park Forest canceled its parade.
Oak Park canceled its fireworks, and Mundelein canceled all Fourth of July activities.
The Lombard, Downers Grove and Woodridge Fourth of July fireworks displays are canceled.
Six Flags has canceled their fireworks show.
The Chicago White Sox said their postgame fireworks celebration is canceled. A moment of silence will be held before the start of the game.
The Chicago Bulls issued a statement on Twitter about the shooting.
Highland Park had a number of Fourth of July events scheduled for Monday.
WATCH: Gov. JB Pritzker speaks on Highland Park shooting
Illinois State Police were on the scene, as well.
The FBI and ATF responded.
Attorney General Merrick Garland has been briefed. Homeland Security officials are gathering more information.
Anyone with tips on the incident is asked to call 1-800-call-FBI or submit online at tips.fbi.gov.
Counseling professionals will be available tomorrow for students, staff and community members at Highland Park High School from 9:00 a.m. to 2:00 p.m. Tuesday, the city said.
"Thinking about seeing all of my students at the parade, today, and just knowing this is something that they witnessed that they will have to process and go through, it's sickening," said Lauren Sachs, a witness.
Sun-Times Media contributed to this report.
ABC News contributed to this report.