Charges are expected to be filed on Tuesday against the suspected gunman in the shooting at a 4 July 4 parade in the Chicago suburb of Highland Park where six people were killed and dozens more wounded, Mayor Nancy Rotering said.
In interviews with TV news outlets, Rotering said the community of 30,000 was still reeling from Monday's attack.
"This tragedy should have never arrived at our doorsteps," she told NBC News. "As a small town, everybody knows somebody who was effected by this directly and, of course, we are all still reeling."
Just a day prior, the streets were decked out in red, white and blue as families watched the annual Independence Day parade. Children waved American flags as parents and grandparents relaxed in folding chairs.
As the parade began rolling through downtown, police said the shooter climbed to the roof of a business using a ladder in an alley and then, without notice, opened fire with an assault rifle at the crowd below.
On Monday evening, police announced that they had a suspect, 22-year-old Robert E. Crimo III, in custody after he surrendered to authorities. Police said they did not know what the motive was for the shooting.
A retired four-star general, who wished not to be named, said he was in the crowd when the gunfire began, and scooped up one of his granddaughters before sprinting for safety to the Sunset Foods grocery store across the street.
"They were scared to death, they didn't know what was going on," he said as he was brought to tears. "I had her up against my chest and she told my daughter later on 'Grandpa's heart was pounding.'"
The 72-year-old man said he was with his family, including his twin grandchildren, at the parade. He said he had served in the military for 30 years. "I thought I was done with this nonsense," he said.
The wounded ranged in age from 8 to 85, including four or five children, police said.
Mass shootings have become recurrent in the United States. Monday's attack came less than two months after a gunman murdered 19 school children and two teachers at an elementary school in Uvalde, Texas, just 10 days after a man shot dead 10 people at a grocery store in Buffalo, New York.
Rotering, the city's mayor, said she knew the suspect when he was a little boy and a Cub Scout and she was a Cub Scout leader.
"What happened? How did somebody become this angry, this hateful?" she said.
Social media and other online posts written by accounts that appeared to be associated with either Crimo or his rapper alias, Awake The Rapper, often depicted violent images or messages.
One music video posted to YouTube under Awake The Rapper, for example, showed drawings of a stick figure holding a rifle in front of another figure spread on the ground.
Rotering said on Tuesday that she did not know where the gun the gunman used came from, but added that it was legally obtained.
"Our nation needs to have a conversation about these weekly events involving the murder of dozens of people with legally obtained guns," she said.
The attack comes as Americans continue debate about gun control and whether stricter measures can prevent the mass shootings that happen so frequently in the United States.
The U.S. Supreme Court said last month that there is a constitutional right to carry weapons in public in a ruling that also made it easier for pro-gun groups to overturn modern gun regulations. Since then, the court has thrown out a ruling by a lower federal court upholding Maryland's ban on assault weapons.
Congress last month passed its first major federal gun reform in three decades, providing federal funding to states that administer "red flag" laws intended to remove guns from people deemed dangerous.
The law does not ban sales of assault-style rifles or high-capacity magazines but does take some steps on background checks by allowing access to information on significant crimes committed by juveniles. read more