https://thesocietypages.org/socimages/2016/05/05/early-research-on-police-body-cameras-supports-use/

The first experimental evidence concerning use-of-force comes from a large study in the Rialto, California Police Department, and the results should encourage advocates of body cameras. The study randomly assigned particular police shifts to wear body cameras (the “treatment”). Police shifts in the treatment condition are associated with reduced use-of-force and citizen complaints against the police were significantly reduced. Shifts in the control condition, in contrast, saw roughly twice as much use-of-force as the treatment condition.

The research so far suggests that body cameras are a promising way to reduce unnecessary use of force.