Chicago police have released a photograph of the weapon used in the Highland Park mass shooting on 4 July, where seven people were killed and dozens injured.
On Monday evening, police arrested 22-year-old Robert “Bobby” Crimo after an hours-long manhunt around the city north of Chicago.
A spokesperson for the Lake County Major Crime Task Force said the suspect used a rifle “similar to an AR-15” from atop a commercial building and fired into a crowd that had gathered for the parade in Highland Park.
On Wednesday night, the police released a photograph of the Smith & Wesson M&P 15 rifle, reported News Nation.
According to prosecutors, the suspect fired more than 80 rounds, reloading three times, before fleeing down a fire escape while disguised as a woman and melting into the crowd.
Authorities added that while he went down the fire escape, the weapon fell out of his bag in an alley.
The rifle was found with three 30-round high-capacity magazines and 83 spent shell casings around the scene.
Authorities initially said they had recovered a rifle from along the Fourth of July parade route, and that they were deliberately withholding further details as they hunted for the gunman.
Officials added on Wednesday that Mr Crimo had confessed to shooting at the Independence Day parade and then fled to the Madison, Wisconsin, area, where he contemplated shooting up another event.
Lake County Major Crime Task Force spokesman Christopher Covelli said Mr Crimo turned back to Illinois, where he was later arrested, after deciding he was not prepared to pull off a shooting in Wisconsin.
In court on Wednesday, an Illinois judge ordered Mr Crimo to be held without bail.
Lake County assistant state attorney Ben Dillon said in court that the shells of 83 bullets and three ammunition magazines were found on the rooftop that he fired from.
“For each individual that was hurt, people can anticipate an attempted murder charge as well as an aggravated battery with a firearm charge,” Lake County state attorney Eric Rinehart said after the hearing, according to CNN.
“Every time he fires a bullet at an individual, he is committing aggravated discharge of a weapon, whether he hit someone or not. There will be many more charges coming in the coming weeks.”
