Chicago suburb officials say gunman had been planning massacre ‘for several weeks’

Officials in the Chicago suburb of Highland Park have said the suspected perpetrator of a mass shooting at a July 4 parade that left at least six people dead and more than 30 injured had been planning the attack “for several weeks”.

In a press briefing on Tuesday, Lake County Sheriff’s Department deputy chief Christopher Covelli told reporters the shooter had legally purchased the firearm used in the massacre somewhere in the Chicago region of Illinois.

Robert E Crimo III, a 21-year-old man who was detained as a “person of interest” on Monday evening after an eight-hour manhunt, remained in custody on Tuesday and is expected to be charged later in the day.

“Some of this is still preliminary so is subject to change as we keep moving forward,” Covelli said. “But we do believe Crimo pre-planned this attack for several weeks.”

Covelli provided further details of how the attack unfolded, noting that the suspect “was dressed in women’s clothing, and investigators do believe he did this to conceal his facial tattoos and his identity”.

Investigators have identified the weapon used in the massacre as a “high-powered rifle”, “similar to an AR-15”. They believe the shooter fired more than 70 high-velocity rounds into the crowd from his rooftop perch.

You are seeing a snapshot of an interactive graphic. This is most likely due to being offline or JavaScript being disabled in your browser.

After he stopped shooting, officials said, Crimo dropped the rifle on the ground and walked to his mother’s house, where he borrowed her car to leave the area. The Bureau of Alcohol, Tobacco, Firearms and Explosives was then able to use the discarded rifle to identify the shooter, who had a second rifle, also legally purchased, in the vehicle when he was apprehended.

Law enforcement officials believe Crimo acted alone but have not yet determined his motive for carrying out the attack, Covelli said.

Covelli clarified that law enforcement had some contact with Crimo in the past, but “nothing of a violent nature”. He said officers had not been made aware of online videos depicting gun violence uploaded by the shooter before Monday’s massacre.

Further details of the attack came as Congress is imposing new federal restrictions on gun ownership after a number of deadly attacks across the country in recent months.

Illinois has some of the tightest gun control laws in the US, requiring universal background checks for purchasers and permits for those carrying firearms.

Highland Park mayor Nancy Rotering told NBC’s Today show on Tuesday that she had been the shooter’s Cub Scout leader when he was a child.

“How did somebody become this angry, this hateful, to then take it out on innocent people?” she said.

“I don’t even want to ascribe it to mental health. I want us to talk about the fact that there are weapons of war on our streets, that people can legally obtain these, and then take out dozens of people. Our community is never going to recover from this wound,” Rotering added.

The attack followed several other recent deadly shootings across the US. In May, an 18-year-old white supremacist was accused of using an assault rifle to gun down 10 black patrons in a supermarket in Buffalo, New York. Later that month, an 18-year-old man fatally shot 19 students and two teachers at an elementary school in Uvalde, Texas.

The bipartisan gun safety bill, which was signed into law by Joe Biden, falls short of policies advocated by the president and other Democratic lawmakers, but it does include more stringent background checks for gun purchases and lets states introduce “red flag” laws to stop dangerous individuals from buying firearms.

The Highland Park attack came less than two weeks after the Supreme Court recognised a constitutional right to carry firearms for self-defence, and struck down a century-old New York state law that required individuals to show “proper cause” to hold a concealed gun in public.

The ruling is set to have significant consequences for the gun control debate.

It has also raised concerns that other states with similar limits on gun licensing — including California, Hawaii, Maryland, Massachusetts and New Jersey — and the District of Columbia could also face legal challenges.