From the U. of Chicago:
University of Chicago Crime Lab
… Between 2015 and 2016, Chicago experienced 58 percent more homicides and 43 percent more non-fatal shootings. Annual increases of this size are not unprecedented among American cities, particularly in recent years, but are rare for a city of Chicago’s size.
One striking feature of Chicago’s increase in gun violence is how sudden it was: as of December 2015, there was no indication that gun violence was on the verge of rising sharply. But in January 2016, homicides and shootings surged relative to their 2015 levels and remained higher in almost every month that followed, threatening 20 years of progress on violent crime in Chicago. …
What caused Chicago’s sudden surge in gun violence in 2016 remains a puzzle. Weather cannot explain the surge in homicides and shootings, since monthly temperatures in 2016 were close to their historical averages. City spending on social services and public education did not change much in 2016 compared to previous years, and while the state budget impasse disrupted funding for many community organizations, this did not seem to change sharply in December 2015.
Another form of police activity that declined in 2016 is street stops. Chicago police recorded over 80 percent fewer stops in January 2016 than they had in November 2015. This drop, from an average of over 50,000 stops per month in 2015 (through November) to approximately 10,000 stops per month starting in early 2016, began a few months before rates of gun violence in Chicago began to increase. What caused the decline is itself unclear.
Several frequently-mentioned candidate explanations—the release of video footage showing the shooting by a CPD officer of teenager Laquan McDonald, announcement of a U.S. Department of Justice (DOJ) investigation of CPD, implementation of an agreement between the City and the American Civil Liberties Union (ACLU) concerning street stops, and a new state law regarding street stops—all happened essentially within a few weeks of each other in late 2015 and early 2016.
Well, there’s your problem(s), Chicago.