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The Supreme Court on Thursday said the lab analyst who testifies at a criminal trial must be the one who performed or witnessed the lab tests in question, the latest decision bolstering the constitutional requirement that defendants be able to confront witnesses against them.

In a 5-4 decision, the court ruled in favor of a New Mexico man convicted of drunken driving who objected when the lab analyst who testified about lab tests had no role in performing them.

The ruling reversed a New Mexico Supreme Court decision in the state's favor.

When Donald Bullcoming's case went to trial on charges he was driving while intoxicated, the main evidence against him was a lab report showing his blood-alcohol level was well above the legal limit for driving.

But instead of calling as a witness the analyst who performed the lab test, the state chose someone else. Prosecutors said the analyst who did the test had been placed on unpaid leave, but did not say why.

Bullcoming objected to the testimony, but the judge allowed it and a jury convicted Bullcoming. The New Mexico high court said the substitute analyst's testimony satisfied the Constitution's cross-examination right.

But, writing for the U.S. Supreme Court, Justice Ruth Bader Ginsburg said the surrogate testimony could not convey what the original analyst knew about the tests he performed.

"The Sixth Amendment does not tolerate dispensing with confrontation simply because a court believes that questioning one witness about another's testimonial statements provides a fair enough opportunity for cross-examination," Ginsburg said.

Justice Anthony Kennedy said in a dissenting opinion that the court was distorting the meaning of the word "witness" because the tests are entirely machine-run and often, as in this case, can be performed after everyone has left for the day.

"In these circumstances, requiring the state to call the technician who filled out a form and recorded the results of a test is a hollow formality," Kennedy said, in an opinion that was joined by Chief Justice John Roberts and Justices Samuel Alito and Stephen Breyer.

Bullcoming's case was important because it might have signaled the court's retreat from a 2004 decision that significantly strengthened the right to cross-examine witnesses. Justice Sonia Sotomayor wrote the decision in February ruling against a defendant in a murder trial who said he had been unfairly denied the chance to cross-examine the victim. Justice Elena Kagan, who did not take part in that case, had no track record on the topic before Thursday.

But they signed onto almost all of Ginsburg's opinion Thursday, a development that Stanford law professor Jeffrey Fisher, Bullcoming's lawyer, called "very reassuring."

As for Bullcoming himself, state courts will now have to determine whether the conviction can stand.

The case is Bullcoming v. New Mexico, 09-10876.