When a mostly white Simi Valley jury in 1992 acquitted four Los Angeles police officers accused of beating Rodney King, the jurors were blamed for ignoring videotaped evidence and igniting the deadliest riots since the Civil War.

Currently, a mostly black jury is under fire for ignoring a mound of DNA evidence and acquitting O. J. Simpson almost without deliberation.

But jurors in both trials were ordinary citizens who performed their civic duty under intense pressure. More worthy of criticism are the questionable decisions of public officials who stacked the deck against the prosecution.

California judges unnecessarily put the trial of the police officers in suburban Simi Valley. Paying as little attention to legal precedents as the jurors would later be accused of doing to the evidence, an appellate court granted a change of venue because of political turmoil and extensive media coverage in Los Angeles in the wake of the King beating.

These were dubious grounds. No change of venue had been granted in a Los Angeles County trial in nearly two decades, even in such notorious cases as the Charles Manson murders.

Stanley Weisberg, the trial judge, compounded the problem by keeping the trial in the same media market. He merely moved it across the county line from racially diverse Los Angeles to Ventura County, where there are few blacks.

In the Simpson trial the prosecution stacked the deck against itself. District Attorney Gil Garcetti, who was elected because of backlash to the riots, had a choice of trying Simpson in downtown Los Angeles or Santa Monica, near Simpson's Brentwood home.

Garcetti amazingly chose a downtown trial even though he knew that the demographics of the Santa Monica area would produce a more diverse jury pool. Like Weisberg, he seems to have been motivated by reasons of convenience. He may also have assumed that the evidence was so overwhelming that it made no difference where Simpson was tried.

But race matters in criminal trials, as in other aspects of American life. Jurors in both cases deny that their verdicts were race-based, but racial perceptions influenced the way they viewed the evidence.

The Simi Valley jury, with 10 whites and no blacks, was composed of people who saw police as their guardians. These jurors pulled over for police cars. They could not understand why King ignored the lights and sirens of a California Highway Patrol car and led police on a high-speed freeway chase.

When the Simi Valley jurors watched the famous videotape in its entirety rather than the truncated version used on television, they found out that King had charged at Officer Laurence Powell, who delivered most of the baton blows. When they also learned from testimony that the accused officers had tried to take King into custody peaceably before any blows were struck, they bought the defense argument that King was responsible for what happened to him.

The Simpson jurors, nine of them African American, had a more hostile view of police. Blacks in Los Angeles have long complained of humiliations at the hands of the LAPD, which doesn't always play by constitutional rules. These jurors dismissed as lies the police testimony that detectives went to Simpson's home to tell him of Nicole Brown Simpson's death; they realized that the real mission was to search the premises.

Such warrantless searches are common, but few murder defendants can afford the legal resources to expose them. Simpson could. The illegal search tainted the prosecution case from the beginning, and the taint became tarnish with the disclosure of detective Mark Fuhrman's racism.

Fuhrman's racist views were well known within the LAPD, and the New Yorker reported before the trial that the defense intended to exploit them. The extent of prosecution knowledge is unclear, but Garcetti could have learned the truth with a single phone call.

Jurors inevitably bring personal experiences into the courtroom, which is why jury diversity is so important. It is often forgotten that even the Simi Valley jury disagreed on a principal charge against Officer Powell, who would have been retried in state court had not the federal government taken over the prosecutions after the riots.

Most analysts of the Simi Valley trial believe the defendants would have been convicted if the same evidence had been presented to a racially diverse jury in Los Angeles. Similarly, a conviction or mistrial might have resulted if the evidence against Simpson had been presented to a racially diverse jury in Santa Monica.

Both verdicts are troubling, but the juries had reasons for their actions. Those who deplore the verdicts as unjust should focus their criticism not on amateur jurors who were doing their best but on elected officials whose faulty decisions produced juries that lacked the balance of diversity.