In addition, recent research has examined the role that body camera video footage plays in court. Drawing from cases of excessive use of force in the federal courts, one study found that BWC evidence can have an impact on summary judgment outcomes in favor of the defendant, but only when the video has a complete depiction of the event. Similarly, a study specific to domestic violence case outcomes found that cases with body camera footage had higher arrest rates, guilty pleas, and guilty verdicts. Both studies, however, found potential evidence of a “CSI effect,” whereby juries expect high-quality footage covering the entire event; in cases for which footage is absent, partial, or of low definition, jurors may be less inclined to view the evidence as persuasive.

Impact on Police Officer Behavior

Studies on the effects of BWCs on officer use of force are perhaps the most plentiful, and they have yielded mixed findings. Lum et al.’s comprehensive meta-analysis of 30 rigorous studies published through 2019 found an average effect of a 6.8% reduction in officer use of force associated with BWCs, but this reduction was not statistically significant. The authors also expressed uncertainty about this impact based on considerable variation in effects across studies. Indeed, a recent and large experimental study of BWCs in New York City found no reduction in use of force. However, a study employing a natural experiment examining over 1,000 police agencies nationwide (to examine fatal use of force) and 96 agencies in New Jersey (evaluating non-fatal use of force) found a 20% decline in non-fatal use of force, a 42% reduction in force resulting in injury, and a 41% reduction in officer-involved homicides among agencies that had adopted BWCs. Most recently, a meta-analysis by Williams et al. used Lum et al.'s data on studies specifically related to use of force and complaints and added Kim and Zimroth et al., recalculating the average effects of these two outcomes. That meta-analysis found an average reduction in use of force of 9.6%, although it should be noted that this effect is primarily due to the inclusion of the large effect found by Kim. We also note that there is debate over whether the Kim study would have satisfied the methodological criteria of Lum et al.'s systematic review. The bottom line is that there continues to be uncertainty as to whether BWCs can reduce use of force, and research has yielded a mix of positive, negative, and null findings. Agency policy on BWC usage varies, as does officer compliance with those policies. These inconsistencies in BWC use may explain the uneven impact of the technology documented in BWC evaluations. For example, while the majority of BWC programs mandate that officers activate their cameras for all interactions with community members, studies have shown that officers primarily activate their cameras when responding to violent or serious property crimes, and that they are more likely to make an arrest if their BWC was activated earlier in the interaction. This variation in when and how BWCs are used by officers may diminish their intended impact. Newer BWC “auto-triggering technologies” that activate cameras when officers exit their patrol car, pull their weapon from its holster, or are in the vicinity of another officer who activates his or her camera, may support improved documentation of police-community member interactions. Other officer behaviors examined by Lum et al. include the impact of BWCs on outcomes such as the volume of arrests and citations, proactive police activities (including traffic and pedestrian stops), assaults and resistance against officers, and calls for police service. As with use of force, researchers did not find a significant impact of BWC use on these behaviors, and study findings were again highly heterogeneous (yielding a mix of positive, negative, and null findings). Zimroth et al. also examined the impact of BWCs on officer stops. This study documented a 38.8% increase in the number of stops reported by officers equipped with cameras, but also found that these stops were less likely to be considered legal or to result in a summons. At first blush, this finding suggests that BWCs somehow led officers to conduct more stops. Instead, however, the authors theorize that officers equipped with cameras were more likely to report stops because they knew those interactions were being documented on video. For example, the Los Angeles Police Department’s Inspector General released a report that noted a significant number of stops captured on BWC video for which there was no corresponding police paperwork. These findings underscore the importance of understanding what types of policies can ensure camera activation and curb underreporting. Another challenge to any evaluation of BWCs is the growth in prevalence of civilian cell phone video and its potential impact on officer conduct independent of BWCs.