Charles Lane, The Associated Press WASHINGTON - The Supreme Court held a rare mid-May oral argument Thursday on the power of police to search private homes without knocking first -- a major privacy-rights case likely to be decided by the vote of the court's newest member, Justice Samuel A. Alito Jr.

At issue in Hudson v. Michigan is the "knock and announce" rule rooted both in the Fourth Amendment to the Constitution and Anglo-American common law. The rule says that, in normal cases, police with a search warrant must first knock and state their purpose, then wait a reasonable period before forcing their way in.

Most federal and state courts that have considered the question have said that courts must exclude evidence seized by police who failed to follow the rule. But in recent years, the Michigan Supreme Court has joined the minority that say no such "exclusionary rule" is required.

When the court first heard oral arguments Jan. 9, Justice Sandra Day O'Connor was still on the bench. But O'Connor stepped down in favor of Alito before the court could issue its opinion.

The court then announced it would hear arguments again; it gave no reason, but since it would have been able to issue a decision if there were still five votes for one side or the other without O'Connor, the most probable explanation is that the court was divided 4-4 and needs Alito, a former prosecutor who built a strong pro-police record as a federal appeals judge, to break the tie.

Liberals on the court openly worried that Michigan's approach would carry the day -- effectively gutting the knock-and-announce rule and, potentially, other restrictions on police searches as well.

Justice Stephen Breyer said that, if the court rules in Michigan's favor, "we'd let a kind of computer virus loose in the Fourth Amendment. I don't know what the consequences would be."

Michigan courts upheld the 2002 drug possession conviction of Booker Hudson, ruling that the officers who burst into his Detroit home three to five seconds after crying "Police! Search Warrant!" would have found crack cocaine in his jeans even if they had knocked and waited.

Under a 1999 Michigan Supreme Court ruling, defendants like Hudson can prevail if only they show that the police's failure to knock directly caused the discovery of the evidence.

Michigan does not deny that the officers technically violated the knock-and-announce rule. It argues rather that, since they had a warrant, their presence in the house was legal even if the way they got inside was not.

Michigan also argues that the knock-and-announce rule can be adequately enforced by private lawsuits for damages against the police, or by internal police discipline, a position echoed by the Bush administration, which supports Michigan.

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