"Between January and December 2017, 28 incidents of mass attacks, during which three or more persons were harmed, were carried out in public places within the United States (see map for locations). These acts violated the safety of the places we work, learn, shop, relax, and otherwise conduct our day-to-day lives. The resulting loss of 147 lives and injury to nearly 700 others had a devastating impact on our nation as a whole. As the uncertainty they caused continues to ripple through our communities, those charged with ensuring public safety strive to identify methods to prevent these types of attacks. To aid in these efforts, the U.S. Secret Service National Threat Assessment Center (NTAC) examined these 28 incidents, to identify key themes for enhancing threat assessment and investigative practices."
United States Secret Service: https://www.secretservice.gov/