You “assume” it’s more likely she had the fake gun. What is that based on? For the cops I know of and have dealt with I can say it’s incredibly likely both ways depending on the area. Some places I have found the police to be honorable and respected. Other places, like parts of California, I have found them to be incredibly corrupt and the most likely scenario for Occam’s razor is it was a plant. This is why citizens demand body cameras on cops, and when they do, the rate of officer involved shootings and misconduct go way down.

I gave you a reason - road rage. Leads to murder all the time. Add to that the natural short fuse and above-the-law attitude of the common pig and you have a pretty solid motive.

Try briefly making physical contact between your car and a police car and see what happens.