 Complete the following phrase:  According to a report released in 2016 by the National Law Enforcement Officers Memorial Fund, 50 U.S. police officers were killed by homicide as of late July, representing a significant increase from the 33 officers murdered in 2015. The report also noted an increase of ambush killings targeting officers, with fourteen incidents recorded. Also in July 2016, there had been two mass shootings targeting police officers in 