In Jennifer Doleac's Brookings article, "Do body-worn cameras improve police behavior?", she describes a randomized control trial in Washington, D.C. that tested the effect of police body-worn cameras on excessive use of force. This study found no effect. What might explain this result?

1. Washington, D.C. has already implemented many policies to reduce excessive use of force, so the margin for improvement might be much smaller than in other cities.
2. The widespread presence of cell phones means that police already act as though they are being recorded without wearing body cameras.
3. The result cannot possibly be true; body-worn cameras must have an effect on police behavior.
4. Body-worn cameras do not change police behavior; that is, police are just as likely to use excessive force when they are being video-recorded as when they are not.

https://www.brookings.edu/blog/up-front/2017/10/25/do-body-worn-cameras-improve-police-behavior/