The annual number of homicides in Baltimore shows a very dramatic break from 2014 to 2015. In the 4 years before 2015, homicides averaged about 150 per year, but in 2015 an later, about 250 per year, a jump of 60%.
Looking within the years 2014 and 2015, we can see when the divergence started. There is a lot of noise in homicide time series, but the big break seems to happen about week 16 or 17 in 2015, the weeks of 19 April through 2 May. There are a lot of possible causes for increases in homicides, but there is one notable event that happened about that time: Freddie Gray was arrested on 12 April 2015, and died on 19 April 2015.