KRASNODAR, Russia -- After deliberating for three hours, a jury of six men and six women voted early last month to acquit Vladislav Kozachenko of the February 2004 murders of a 25-year-old woman who ran a prostitution ring in this southern Russian city and her 39-year-old lover.

Mr. Kozachenko thanked the jury from behind the bars of the courtroom cage where he sat during the three-week proceeding. But the relief visible on his face must have been tempered by the fact that twice before he had heard different juries pronounce him not guilty of the same crime. And twice before, prosecutors had refused to accept the verdict and brought him back to trial.

"I hope it's third time lucky for me," said Mr. Kozachenko, 36, after his release. "Maybe they will let me go now and look for the real murderer."

That remains to be seen. Prosecutors immediately vowed to appeal the verdict to the Russian Supreme Court and secure a new trial. "We are convinced the murder was committed by him," said Natalia Kalikanova, the lead prosecutor in Kozachenko's third trial. "He's guilty. We cannot leave an unlawful verdict in force."

Twelve years after its introduction as a landmark legal reform in a country just emerging from communism, the jury system remains the object of suspicion, even contempt, among prosecutors and some judges in Russia. "I would abolish it," Ms. Kalikanova said flatly.

Juries were introduced as part of an almost complete overhaul of the former Soviet legal system in the 1990s. On paper, it drew widespread admiration from government leaders. But scholars and human rights activists charge that the system still reflects the values of the old communist-era courts, in which a presumption of guilt prevailed. To them, the jury system's failure to take root and recent proposals to scale it back are part of a broader rollback of democratic practices and institutions in President Vladimir Putin's Russia.

Under Russian law, double jeopardy is not prohibited. Prosecutors, as well as defendants, can appeal verdicts, and almost all jury acquittals are appealed. In the past five years, between 25 percent and 50 percent of not-guilty verdicts returned by juries were reversed by the country's Supreme Court, according to annual court statistics and analyses by Russian legal scholars.

"Nobody thought so many verdicts would be overturned," said Sergei Nasonov, a Moscow State Law Academy professor of criminal law, who has written a book on jury trials in Russia. "The reasons for overturning jury verdicts were supposed to be very limited, but the Supreme Court has interpreted the law very broadly. A jury verdict is hardly ever the final word."

Still, juries remain a significant check on the power of the state. Prosecutors were long accustomed to getting automatic guilty verdicts when they decided to go forward with a trial. Year after year, only between 1 percent and 2 percent of defendants are acquitted in bench trials in Russia, statistics show, compared with about 15 percent in jury trials.

In Krasnodar, there have been years when not a single person was acquitted by a judge, but nearly a third of defendants in jury trials were acquitted, according to regional court statistics.

Often, jury verdicts are overturned on highly technical grounds.

Mr. Kozachenko's first not-guilty verdict, in September 2004, was reversed because the judge failed officially to notify a relative of one of the victims of his right to make a final statement to the jury, which voted 11 to 1 to acquit. In Russia, a jury verdict is decided by a majority vote of the panel.

The second acquittal, in April, was overturned because of errors in the judge's written charge to the jury, which had been unanimous in finding Mr. Kozachenko not guilty.

After the 8 to 4 vote in favor of the defendant this month, Ms. Kalikanova, the lead prosecutor, said she discovered that some jurors on the panel "concealed certain information about themselves, criminal records and previous service in the police." The post-trial discovery of such information is frequently invoked in appeals to the Supreme Court.

"When a not-guilty verdict is passed, the prosecutors begin to dig around," said Judge Nina Stus of the Krasnodar regional court, who has presided over more than 100 jury trials. "It's a card prosecutors keep up their sleeve in case there is a not-guilty verdict."

Pressure is mounting to limit those eligible for a jury trial.