The Legal Framework for Evidence-Based Policing in the United States

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Document Type

Book Chapter


This book chapter examines the existing legal framework for evidence-based policing in the United States, identifying three areas in which contemporary constitutional and sub-constitutional law create obstacles to evidence-based policing and exploring how reforms to the legal system could instead create incentives.

First, constitutional decision-making by the Supreme Court is often predicated on the justices’ understanding of police practices and the environment in which officers operate. The Court has proven willing to rely on its own factual assumptions even when there is a noticeable lacuna of evidence that support its assertions. With the improved availability of information, evidence-based policing can offer the Court and other judicial decision-makers a more robust and accurate understanding of the world that they are regulating. In the same vein, courts can inspire police agencies to adopt evidence-based practices by relying more heavily on reliably gathered data rather than anecdotes and speculation.

Second, when officers testify, they are often asked to provide both their first hand observations and their professional opinions about various matters. Such opinions, including expert opinions, are typically grounded in officers’ “training and experience.” In many cases, however, that training and experience may not support the inference of reliability that expert testimony properly demands. With a rigorous and methodologically sound approach to developing information, opinions grounded in evidence-based practices and instruction would be substantially more dependable than opinions based on more traditional forms of instruction.

Third and finally, the legal rules that restrict or permit the introduction of a variety of other forms of evidence can be leveraged to encourage evidence-based policing practices. In the absence of an evidence-based approach to analyzing forensic evidence, eyewitness identification, interrogation procedures, and other sources of information, policing as an industry has had little reason to keep abreast of best practices. Through their adoption of an evidence based inquiry, courts are in a position to create incentives that could dramatically improve police procedures.