Bodycam footage released by authorities on Thursday showed officer Eric Stillman, 34, firing a single shot at Adam Toledo following an on-foot chase.
A still frame taken from the video recording showed that the youth was empty-handed when Stillman shot him once in the chest at around 3am on March 29.
Police, who were responding to reports of violence in the area, say the boy had a handgun on him before the shooting.
The release of the footage and other investigation materials comes at an already fractious time, with the ongoing trial in Minneapolis over the death of George Floyd and the recent police killing of another Black man, Daunte Wright, in a suburb of the same city.
- ‘The Circle’ apartment is a catfish - here’s where it’s actually filmed
- The 18 best memes and reactions as M&S declares legal war on Aldi over Colin the Caterpillar
- Reddit just realized that Jerry Seinfeld’s TV apartment defies the laws of science
- 20 jokes only very intelligent people will understand
- Ex-McDonald’s employee reveals Sundays are the worst day of the week to order
The shooting of Adam has been met with fury and desperation on social media, as people call for an end to perceived police brutality in the US – particularly against Black and Hispanic victims.
Congresswoman Alexandria Ocasio-Cortez is among those calling for justice, she tweeted:
Her criticism referred to comments made by a prosecutor during a court appearance, claiming that Adam had been holding a gun at the time of the shooting.
The Cook County State’s Attorney’s office later issued a statement acknowledging the error.
“An attorney who works in this office failed to fully inform himself before speaking in court," they said.
"Errors like that cannot happen and this has been addressed with the individual involved. The video speaks for itself."
Here’s how other public figures have responded to the disturbing footage, both in America and across the world:
The bodycam video shows that 19 seconds elapsed between the moment Stillman got out of his squad car and when he shot Adam.
During this time, he chased the 13-year-old on foot down an alley. As the boy slowed down, Stillman ordered him to show his hands.
As Adam turned toward the camera, Stillman said: "Drop it!"
Repeating the command, he suddenly opened fire and the adolescent fell to the ground.
While approaching Adam, Stillman called for an ambulance as he implored him to "stay awake".
As other emergency service workers arrived, a fellow officer said he couldn’t feel a heartbeat and began administering CPR. But it was too late to save the child’s life.
In a lengthy email, Stillman’s lawyer Tim Grace claimed that the 13-year-old left the officer with no choice but to shoot.
"The juvenile offender had the gun in his right hand ... looked at the officer which could be interpreted as attempting to acquire a target and began to turn to face the officer attempting to swing the gun in his direction," Grace wrote.
"At this point the officer was faced with a life threatening and deadly force situation. All prior attempts to de-escalate and gain compliance with all of the officer’s lawful orders had failed."
Adeena Weiss-Ortiz, an lawyer for Toledo’s family, told reporters the footage and other videos "speak for themselves".
She said it is irrelevant whether Adam was holding a gun before he turned toward the officer.
"If he had a gun, he tossed it," she said.
"The officer said: ‘Show me your hands.’ He complied. He turned around."
Chicago mayor Lori Lightfoot has called on the public to keep the peace in anticipation of unrest in the city.
Demonstrations have already begub to take place across the city.
"We live in a city that is traumatised by a long history of police violence and misconduct," Lightfoot said.
"So while we don’t have enough information to be the judge and jury of this particular situation, it is certainly understandable why so many of our residents are feeling that all too familiar surge of outrage and pain.
"It is even clearer that trust between our community and law enforcement is far from healed and remains badly broken."
The Chicago Police Department typically does not release the names of officers involved in such shootings this early on in an investigation.
However, Stillman’s name, age and race were listed in the investigation reports released on Thursday.