Authorities in Kansas City said that the mass shooting that unfolded amid people at the Chiefs’ Super Bowl celebration appeared to stem from a dispute between several people.
Police Chief Stacey Graves said that 22 people injured in the shooting ranged between the ages of eight and 47 years old, half of whom were under the age of 16.
A mother of two was also killed.
Three people were detained, including two juveniles, and firearms were recovered during the mayhem, police said.
Investigators are also calling for witnesses, people with mobile phone footage and victims of the violence to call a dedicated hotline.
Ms Graves said at a news conference: “We are working to determine the involvement of others. And it should be noted we have recovered several firearms. This incident is still a very active investigation.”
The shooting outside Union Station occurred despite the presence of more than 800 police officers who were in the building and nearby, including on top of nearby structures, said Mayor Quinton Lucas, who attended with his wife and mother and ran for safety when the shots rang out.
“Parades, rallies, schools, movies. It seems like almost nothing is safe,” Mr Lucas said.
However, he also added that he doesn’t expect to cancel the upcoming St Patrick’s Day parade.
“We have parades all the time. I don’t think they’ll end. Certainly, we recognised the public safety challenges and issues that relate to them,” Lucas said.
University Health spokesperson Leslie Carto said two of the eight gunshot victims brought to the hospital are still in critical condition and one is in stable condition. The other five have been discharged.
The hospital also treated four people from the rally who had non-gunshot injuries. Three of those patients were discharged, Ms Carto said.
Stephanie Meyer, chief nursing officer for Children’s Mercy Kansas City, said it was treating 12 patients from the rally, including 11 children between the ages of six and 15, many of whom suffered gunshot wounds.
All were expected to recover, she said.
When asked about the condition of the children, Ms Meyer responded: “Fear. The one word I would use to describe what we saw and how they came to us was fear.”
St Luke’s Hospital spokesperson Emily Hohenberg said one gunshot victim at the hospital remains in critical condition.
Four people who suffered injuries while fleeing the aftermath of the shooting were treated and released.
Chiefs trainer Rick Burkholder said he was with coach Andy Reid and other coaches and staff members at the time of the shooting, and that the team was on buses and returning to Arrowhead Stadium.
“We are truly saddened by the senseless act of violence that occurred outside of Union Station at the conclusion of today’s parade and rally,” the team said in a statement.
President Joe Biden, who was briefed on the shooting and received updates throughout the day, said the tragedy “cuts deep in the American soul” and called for Congress to take action to prevent gun violence.
“And I ask the country to stand with me,” Mr Biden said in a statement.
“To make your voice heard in Congress so we finally act to ban assault weapons, to limit high-capacity magazines, strengthen background checks, keep guns out of the hands of those who have no business owning them or handling them.”
Throngs had lined the parade route before the shooting, with fans climbing trees and street poles or standing on rooftops for a better view.
Players rolled through the crowd on double-decker buses, as DJs and drummers heralded their arrival.
