I think this is the incident Freeman is referencing, a Dallas shooting in July 2016 that killed 5 cops and wounded 7 others plus 2 civilians.
Officials said they had found no evidence that the gunman, Micah Johnson, 25, had direct ties to any protest or political group, either peaceful or violent, but his Facebook page showed that he supported the New Black Panther Party, a group that has advocated violence against whites, and Jews in particular.
Johnson fled to a parking garage, where a standoff lasted until
the police killed him Friday morning with an explosive delivered by a remote-controlled robot...
During the standoff, Mr. Johnson, who was black, told police negotiators that “he was upset about Black Lives Matter,” Chief Brown said. “He said he was upset about the recent police shootings. The suspect said he was upset at white people. The suspect stated he wanted to kill white people, especially white officers.”
https://www.nytimes.com/2016/07/09/us/dallas-police-shooting.html