https://supreme.justia.com/cases/federal/us/471/1/"Under the Fourth Amendment of the U.S. Constitution, a police officer may use deadly force to prevent the escape of a fleeing suspect only if the officer has a good-faith belief that the suspect poses a significant threat of death or serious physical injury to the officer or others."
This appears to be a justified shooting by the officer if the subjects had been firing the gun off in public prior to the arrival of the police. There have been a lot of bad police shootings/encounters, but this does not appear to be one of them. Even if the subjects had been firing the gun into the air and may not have had the specific intent to harm someone, they still had the general intent to break the law by firing the gun, and it is completely possible that they could have killed another person by firing the gun in a heavily populated urban area.
Many people often get very emotional about situations like this without fully understanding the laws. Also, many people don't understand the requirements of a police officer. In the situation shown in the video, the officer does not have the opportunity to wait for backup to arrive on scene or attempt to box the suspect in, due to the quickly fleeing suspect. The suspect is fleeing with a firearm that they were reported to have been discharging in public and it is the officer's duty to stop the threat. If the officer does not do everything reasonable within their power to stop the threat, they can be charged with failure to take action. They can be held further responsible if the fleeing suspect continues to commit crime, harms another person(s), etc. due to the officer's failure to take action and stop the threat, Do some laws need to be changed? Maybe, but Tennessee vs. Garner is the major case law that we currently have regarding a fleeing suspect who is an imminent threat to the public.
It's horribly sad that a young person died, but a 13 year old with a gun can kill someone with said gun just the same as an adult can kill a person with a gun. That said, policing in a city like Chicago is a dangerous and thankless job and I suggest that every single person who is Monday morning quarterbacking without any first responder/military experience, please contact your local police department and request to take a ride along with an officer. Police officers confront the people and situations that the general public is afraid to confront. They see horrible, disgusting, heartbreaking things on a daily basis that you cannot un-see. On your best day or your worst day, 24/7 365, police officers are the only people that are on-call for any situation and are required by law to respond if you request their presence. There are some bad officers, but the majority are honest, hardworking, want to do right by the public, and want police and justice system reform just like the rest of the population does.