The crime was brazen, occurring just two blocks from Chicago Police Department’s Bronzeville headquarters. And on Friday, police arrested the person who, they say, was aiming at a rival gang member but killed city 311 operator Yvonne Nelson. He’s a juvenile, 15 years old at the time of the May 20 crime, so his identity was not released. Now 16, he’s charged with first-degree murder and aggravated battery with a firearm, and police will seek to have him charged as an adult. The teen was on probation for a series of 2014 robberies committed with a BB gun, Police Supt. Eddie Johnson said at a news conference.