The 21-year-old man accused of opening fire on a crowd celebrating US Independence Day in a suburb of Chicago planned the deadly attack for weeks, police said at a press conference on Tuesday, reported DW, quoting news agencies AP and AFP.
Seven people were killed and more than 30 others were injured in the attack on Monday, which took place in the suburb of Highland Park during celebrations for July 4th.
On Tuesday, authorities reported the death of a seventh person who died after being hospitalized.
Suspect charged with murder
The alleged shooter was later charged with seven counts of first-degree murder, prosecutors said.
Lake County State's Attorney Eric Rinehart said the suspect will eventually face "dozens of more charges centered around each of the victims."
If convicted, the man could face a mandatory life sentence without parole, Rinehart added.
Gun was purchased legally
After taking position on a roof overlooking the holiday parade route, the suspect fired 70 rounds into the crowd below, authorities said.
The suspect also took pains to try and conceal his identity — trying to cover up facial tattoos and wearing women's clothing to try and escape.
"He brought a high-powered rifle to this parade," police spokesman Chris Covelli told reporters. "He accessed the roof of a business via a fire escape ladder and began opening fire."
Authorities confirmed that the shooter legally purchased the gun used in the attack, adding that it was similar to an AR-15 rifle.
The suspect also possessed other weapons, including another high-powered rifle, police said, despite authorities having been called to his home twice in 2019 for threats of violence and suicide, police said.
He also appeared to target victims at random, and police do not suspect there was any religious or racial motive.
As Highland Park is a predominantly Jewish neighborhood, there were initial concerns about a potentially antisemitic motive.
Police plan to announce formal charges against the suspect later on Tuesday.
What happened during the attack?
Local families had gathered in Highland Park to watch the local Independence Day parade — which is a July 4 tradition across the US.
Survivors and witnesses said they initially mistaken the shots for the sound of fireworks.
"The people who were gone were blown up by that gunfire," David Baum, a doctor whose child was due to march in the parade, told CNN.
"The horrific scene of some of the bodies is unspeakable for the average person," he added.
Bicycles, folding chairs, strollers and US flags littered the ground of the crime scene — all left behind when parade-goers scrambled to leave the scene.
The suspect fled the scene and managed to evade capture. Authorities launched a massive manhunt for the 21-year-old and he was later taken into custody.
Highland Park, a community of 30,000 people, is located north of downtown Chicago and situated on the shores of Lake Michigan.
Gun violence in the US
The shooting comes amid a spate of mass shootings in the US.
Last month, US President Joe Biden signed the first major federal gun reform law in three decades.
US lawmakers reached the bipartisan agreement on gun control only weeks after a gunman in Buffalo, New York, opened fire on shoppers in April killing 10 people in what has been called a racist shooting.
Shortly afterwards in May, a shooter killed 19 children and two teachers at an elementary school in Uvalde, Texas.
Gun-related killings in the US are higher than in most other high-income countries. In 2019, for example, 4.12 people per 100,000 were killed by guns, while only 0.5 were killed in Canada.