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Less than a day after news broke that the NYPD would be moving up the start date of a pilot program to outfit its officers with cameras, a Staten Island grand jury announced it would not be indicting the officers who killed Eric Garner. This naturally led many to wonder aloud about the efficacy of body cameras. Garner’s death, after all, was recorded by a bystander, so why would body cameras have made a difference?

Based on both the limited research we have so far into how body cameras modify behavior and the theory underpinning their use, though, there are some solid, if preliminary, reasons to believe body cameras could prevent cases like this in the future.

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Since body cameras are relatively new technology, and since some police departments have been less than enthusiastic about adopting them, there is not a great deal of data to sift through at the moment. But we do have some early results. Perhaps most famously and rigorously, Rialto, California, ran a yearlong study in which 54 of its officers were randomly assigned to either wear a camera or not wear one each shift. As the Guardian reported last year, “after cameras were introduced in February 2012, public complaints against officers plunged 88% compared with the previous 12 months. Officers’ use of force fell by 60%.” This echoes early data from the few other comprehensive studies that have been conducted (PDF), including one in Mesa, Arizona.

It’s encouraging, of course, but the real test is going to be what happens when larger police departments embrace this technology. We’ll know more soon: As the Times reported last year, Albuquerque, Fort Worth, and Oakland now have their officers wear cameras. And in addition to the NYPD, the LAPD, Chicago PD, and Metropolitan Police Services in London are all undergoing pilot studies.

What’s key to realize about these cameras in the context of the Garner case is that their presumed effects only kick in when officers know they’re being watched all the time. The authors of the Rialto paper were clear about this:

We hypothesize that portable cameras would go beyond the limited impact that CCTVs have had on expressive acts of violence in public spaces. CCTV cameras were found to be weak behavior modifiers not because of a flaw in the self-awareness paradigm or the deterrence theory. Rather, the level of certainty of being apprehended necessary for the self-awareness mechanism, which would lead to socially-desirable behavior, is not high enough in CCTV. If cameras are expected to influence behavior and to serve as cues that social norms or legal rules must be followed, then the cue “dosage” of awareness must be intense. Mobile cameras are likely to have this effect.

So as tragic as Garner’s death was, it might be incorrect to extract any broader lessons from it about police body cameras. The effects of these cameras may only kick in, or kick in fully, when officers know they’re being watched in every one of their interactions with the public, and it could be the case that these changes in behavior take time — if police are in the habit of acting in an aggressive or confrontational manner with citizens, in other words, the sudden presence of bystanders with cameras might not make a difference. (This ties into a long line of research, much of which is summed up nicely in Mark Kleiman’s book When Brute Force Fails, showing that one of the best ways to change criminal behavior is to ratchet up the odds that the perpetrator will be caught — the same logic can be applied to police.)

None of this means body cameras will permanently fix relationships between police and citizens in places where that relation is strained. “It’s truly not a panacea and at least in my mind, the money used for cameras would be much better used if the money were allocated for screening for recruitment and selection and then proper training,” said Maria Haberfeld of the John Jay College of Criminal Justice. “Because if you have the right people doing this job, and people are properly trained, you don’t need the cameras.”

But between the early evidence that the cameras reduce violent incidents between police and citizens, as well as their ability to sort out what happened in cases like Garner’s — whether or not the justice system then does its job — it certainly seems likely that the momentum for officers to wear cameras is only going to build.