Gina Holland has a report on the oral argument this morning in an interesting Fourth Amendment case, Hudson v. Michigan. The case considers the scope of a suppression remedy for a police officer's failure to follow the "knock and announce" requirements that the Supreme Court has recently held are required by the Fourth Amendment when the police execute a warrant. For a summary of the case, see this helpful post from SCOTUSblog.

  I haven't followed Hudson closely enough to have specific views of it, but the case does bring up some of the broader dynamics of Fourth Amendment law that may be worthy of more general rumination. Specifically, I think Hudson illustrates some of the difficulties inherent in devising a remedy in complex systems. Here's my thinking. Imagine you're a Justice who really values the knock-and-announce rule and wants to make sure the police follow it. Your instinct will be to impose a strict requirement, such that slight deviations from the rule lead to suppression of the evidence obtained. Your thinking will be that a strong remedy means that the rule will be followed. Greater judicial scrutiny will bring greater compliance with the rule.

  Perhaps, but perhaps not. The problem is that the knock-and-announce rule has to coexist with all the other rules that govern searches, and any one rule may end up exerting an unintended hydraulic effect on police behavior. Consider how the knock-and-announce remedy will coexist with the longstanding Fourth Amendment preference for warrants. As precedents like Illinois v. Gates suggest, the Supreme Court has generally tried to encourage warrants by providing less post-indictment judicial review of searches pursuant to warrants than warrantless searches. The idea is to give police officers an incentive to get warrants: Officers know that the chances their searches will be upheld are much greater if they get warrants, so they'll get warrants more often.

  A tough knock-and-announce rule may threaten that preference, because the knock-and-annouce rule does not apply at all to warrantless searches. As a result, the greater the judicial scrutiny on the knock-and-announce rule, the more the police will look for alternatives to warrants. At the margins, at least, ratcheting up the protections of the knock-and-announce rule may have the unintended consequence of lessening judicial oversight by encouraging more warrantless searches. As a result, crafting the remedy for knock-and-announce violations is much harder than just picking the value to be served; to have the desired effect, the remedy has to fit within the regime of preexisting legal rules.