Adam Liptak has an interesting story in today's New York Times about the so-called
exclusionary rule, the rule of criminal procedure instructing (in simplified form) that evidence acquired by the police in violation of investigatory rules cannot be used in a prosecution.
The United States is essentially unique among nations in having a mandatory exclusionary rule: The obvious question is, why? Liptak's article includes a short quote from me on this issue, and I thought I would blog some more thoughts on it.
There are a few reasons why the United States has an exclusionary rule, but I think the most important is that criminal procedure rules in the United States are mostly judge-made.
The courts make the rules in the form of interpretations of the Fourth, Fifth, Sixth, and Fourteenth Amendments. That's largely unique among nations. In most countries, investigative rules come mostly from legislatures, not courts.
In my view, the fact that criminal procedure rules are judge-made led fairly directly to the exclusionary rule.
Put simply, the exclusionary remedy is the one remedy that judges can completely control.
There are a variety of ways to enforce rules of criminal investigations, such as lawsuits, criminal prosecutions, and internal discipline. But all of these alternatives tend to require the cooperation of other branches. The rules governing civil lawsuits are largely under the legislature's control. Legislatures can regulate jurisdiction, create procedural hurdles, limit damages, and the like. And criminal prosecutions and internal discipline require the cooperation of the executive branch. Someone in the executive branch needs to see the violation as a major problem and needs to take action to enforce the law.
In contrast, the exclusionary rule does not require the cooperation of any other branches. The same courts that create the rules control the remedy. As a matter of history, I think that explains why we have an exclusionary rule: judges needed a way to enforce judge-created rules even when they were unpopular and didn't have buy-in from other branches. The exclusionary rule provided a way — and perhaps the only way — to do that.
Finally, let me stress that this explanation is descriptive, not normative.
That is, it describes why I think judges did what they did, but it doesn't take a position on whether the judges did so appropriately or whether they read the Constitution correctly.
If there is interest in the normative question, let me know in the comment thread and I'll consider a follow-up post.