The millions of tweets shared on Twitter daily are a rich resource of public sentiment on countless topics. In the wake of highly publicized officer-involved shootings, many people take to social media to express their opinions, both positive and negative, of the police. We collected millions of public tweets and employed machine learning to explore whether we can measure public sentiment toward the police. Specifically, we examine how public sentiment changed over time and in response to one high-profile event, the 2015 death of Freddie Gray in Baltimore. While accounting for the larger trends in the public image of the police on Twitter, we find that sentiment became significantly more negative after Gray’s death and during the subsequent protests.