Even as nearly 70 major U.S. city and county police forces have begun outfitting their officers with body cameras, departmental policies limit the cameras ability to bring accountability and transparency to law enforcement, according to a study published Tuesday .

Amid the ongoing uproar over police shootings, police reform activists and law enforcement officials have touted body cameras as a tool that can help keep cops and civilians honest. Supporters argue that the devices create objective, first-hand accounts of police encounters, which encourage good behavior on both sides and serve to clarify what happened should interactions go awry.

That sounds good in theory. But the cameras benefits are less clear in practice.

A new body camera scorecard from the Leadership Conference, a civil rights coalition, and Upturn, a firm that works on technology policy issues finds deficiencies in police department policy nationwide. The report grades the policies in 75 departments, including every major city that has begun to deploy body cameras as well as several large counties and smaller jurisdictions. No departments policy receives a perfect rating, and almost all fail across multiple metrics.

The scorecard looks at a range of criteria, beginning with the accessibility of body camera policies. Police departments in some major cities including Boston, Cleveland, Dallas and Detroit are still failing in the basic step of making their policies available to the public online.

The report finds pervasive problems with when officers use their body cameras and how they handle the footage after it is captured. Although most of the departments have developed clear policies outlining which incidents its officers must record, they generally dont require officers to provide concrete justifications should they fail to record those incidents. Most departments have weak or, in many cases, non-existent rules prohibiting tampering with or other unauthorized access to recorded footage.

Under these policies, officers in many departments have failed to record critical incidents . In other cases, key footage has mysteriously gone missing .

Only three major departments in Cincinnati, Las Vegas and Washington expressly allow individuals who are filing misconduct complaints against the police to view all relevant footage. Elsewhere civilians are left at a disadvantage when they try to seek recourse for alleged abuse.

The overwhelming majority of departments do allow or even encourage officers to review body camera footage before filing their initial incident reports or statements. This process can taint evidence-gathering by altering an officers memory of an event, according to an accompanying study titled The Illusion of Accuracy.

This practice will make it more difficult for investigators, internal affairs, and courts to accurately assess what occurred and whether an officers actions were reasonable given what he or she perceived at the time, the authors of the study write. Unrestricted review policies undermine longstanding principles of procedural justice, violate the law enforcement communitys best practices for preserving eyewitness evidence, and threaten to erode community trust.

The authors argue for a two-step system of clean reporting, in which officers write their initial incident report before reviewing any footage, after which theyre allowed to review video and file a supplemental report.