John DeCarlo, a former police chief and an associate professor of criminal justice at the University of New Haven, said that he reminds police officers to treat everyone they encounter with respect, from mundane interactions to very intense ones. Everyday encounters, like seeing an officer in a gas station, shape people’s overall perceptions of the police, he said. “We have an innate fear of police to begin with,” Mr. DeCarlo said. “It’s about treating people how you want to be treated.” Mr. DeCarlo was startled as he watched the security footage of the off-duty Buena Park police officer. “Oh my goodness,” he said as he watched the officer retrieve his gun. “Holy mackerel.” He said that the officer violated the most basic rules governing the use of force by the police. No matter the situation, officers should issue verbal commands first. Pulling out a gun should be a last resort. “What the officer did was incredibly inappropriate,” he said.