In both tragedies of domestic violence and alleged police brutality, the victim can be silenced. Cameras can’t. In a domestic violence incident, the victim can be silenced through the psychological trap of the relationship. In cases of alleged police brutality, victims can be silenced through death. So let the cameras talk.

On July 24, the NFL suspended Ray Rice for two games in the wake of aggravated assault charges stemming from domestic violence against his then-­fiancee, now-wife Janay Palmer. On Sept. 8, the NFL banned him indefinitely from the league. Only one thing changed after the NFL had completed its initial investigation — TMZ released the video of Rice’s knockout punch in the hotel elevator to the public. Pressured to take further action, the Ravens punished and the NFL re­-punished Rice to avoid a public relations nightmare. For once, the executives doling out the repercussions could not ignore the realities of domestic violence.

While domestic violence is an inherently vicious act, the visual accompaniment exposed the ruthlessness of Rice’s actions. The words “domestic violence” are now accompanied by an image of brutality. The camera spoke to the violence of Rice’s punch in a way that mere words could not.

As the investigation into the death of Michael Brown in Ferguson, Mo., unfolds, the lack of video evidence is unsettling, as police officer and witness testimony are creating a disputed timeline of events. Darren Wilson, the police officer who shot and killed the 18-­year­-old Brown, says Brown bum­ rushed him, fought over his gun, and was then preparing to attack again. A witness says the officer was the aggressor and that the unarmed Brown turned to surrender before he was shot six times while his hands were raised. Although cameras may not be completely objective, they provide independent evidence, integral to a comprehensive investigation.

The Rice domestic violence incident and the Brown death have their differences. First, even before the video was released, the Rice incident involved substantially less disagreement over the events in the elevator. In both instances, the victims can not or will not be a vocal advocate for their case. So it is only the presence of a video that allows one of those voices to be heard.

Cameras have been playing an increasingly critical role in changing interactions between law enforcement and the community. A 2013 study revealed that wearing cameras was associated with dramatic reductions in complaints against officers and use­-of­-force in the Rialto, Calif., police department. The authors conclude: “The findings suggest more than a 50 percent reduction in the total number of incidents of use -of­-force compared to control ­conditions, and nearly 10 times more citizens’ complaints in the 12­months prior to the experiment.”

A small number of police departments across the country utilize body­-worn cameras. But 39 percent of local police departments lack the less intrusive dashboard cameras. While a few of the 18,000 police departments across the country have started to equip their officers with body­-worn cameras, municipally instituted policies are not enough.

In counties like St. Louis, with over 80 police departments, local departments have taken a haphazard and unsupervised approach to using camera technology. The Ferguson police department had dashboard cameras, but due to installation costs, they sat in storage. Furthermore, local policies provide insufficient oversight to mitigate privacy concerns that accompany camera­-related police tactics. Instead of patchwork policies, state and federal legislation is necessary to ensure that all police departments are equipped with dashboard and body-worn cameras.

The footage of Ray Rice’s brutal assault reveals the urgent need for body­-worn cameras on cops to capture independent, visual evidence in incidents that usually hinge on testimonial proof. This incident has made it clear: Cameras matter.

Jaimie McFarlin is a current third­-year student at Harvard Law School (Class of 2015).

This article is republished with permission of the author, and originally appeared in the Boston Herald.