Forensic errors, mistaken eyewitness identifications and false confessions have led to wrongful convictions for serious crimes like rape, murder and kidnapping in the United States. Since 1989, 198 convicted felons have been cleared based on DNA evidence, nine in Pennsylvania.

The state's exonerated inmates served more than 140 years in prison, an average of more than 15 years each, for crimes they did not commit.

Prompted by these exceptional cases, the state this week convened a commission of judges, prosecutors, defense lawyers, law enforcement officers and victims' advocates to study the causes of erroneous convictions and make recommendations for preventing them.

The advisory committee includes Allegheny County District Attorney Stephen A. Zappala Jr., public defender Michael J. Machen, police Commissioner Charles W. Moffat, Common Pleas Senior Judge Robert E. Colville as well as an exonerated death row inmate, a Johnstown priest, a representative from the state attorney general's office and Philadelphia District Attorney Lynne M. Abraham.

The project is chaired by John T. Rago, a Duquesne University law professor and director of the Cyril H. Wecht Institute of Forensic Science and Law, who proposed the extensive study to its sponsor, Sen. Stewart J. Greenleaf, R-Montgomery.

Mr. Greenleaf said he was moved to re-examine the criminal process when he learned that a Pennsylvania death row inmate, Nicholas Yarris, had spent 21 years in prison and two others had been serving life terms when DNA evidence excluded them as possible culprits and judges wiped out their convictions. He said it may not be possible "to change the process so that never again will an innocent person be found guilty in our courts," but said he hoped to "make it as best as human beings can."

"Justice is served when a guilty person is convicted, but justice is also served when an innocent person is exonerated. And certainly justice is not served by convicting an innocent person," he said.

With this study, Pennsylvania joins a handful of states that have set up advisory groups to review wrongful convictions.

Mr. Rago sees it as an opportunity to improve due process and fortify investigators' and prosecutors' capacity to present judges and juries with reliable evidence of proof beyond a reasonable doubt that a defendant is guilty. The committee will recommend policy changes after examining a broad range of factors that might influence wrongful convictions.

Advances in social science -- such as improved procedures for witness identification -- and lab science have made it easier to exonerate wrongfully convicted prisoners. Other defendants are mistakenly found guilty because of police or prosecutorial misconduct or simply poor lawyering.

There are lessons to be learned in cases where a single eyewitness put an innocent defendant in prison or in older cases where crime labs did not have the benefit of modern technology to test blood, hair, saliva or other biological evidence.

"With 2.5 million people incarcerated in the U.S., can anybody with a straight face say that they're all guilty? No more than you could say that they're all innocent," Mr. Rago said.

The commission of 40 members will review the cases of the 198 exonerees. Its goal is to identify the most common causes of wrongful convictions and develop policy recommendations. One critical issue will be protecting the rights of victims in the process and making sure they are not revictimized when their cases are reopened.

Given the diversity of the group, Mr. Machen, of the county public defender's office, said he was impressed with the level of dialogue among members at their first all-day meeting Thursday in Harrisburg.

"People were listening to each other and trying not to draw lines in the sand," he said.

Some prosecutors, victims rights groups and law enforcement officials have criticized such commissions for overemphasizing the rights of defendants and neglecting the impact of crime on victims and communities. But proponents say the objective of a wrongful conviction commission is not to go back and assign blame in old cases but to improve the system to everyone's benefit.

"Nobody wants the police or prosecution or the court system to be misled into pursuing an innocent person when trying to solve a very serious crime. The idea behind an innocence commission is that nobody benefits from a wrongful conviction. Not the victim, not the public, not the judge, jury, prosecutor, police, nor certainly the person who was wrongfully convicted," said Stephen Saloom, policy director at the Innocence Project in New York.

The Innocence Project, founded in 1992, is a legal and policy organization dedicated to exonerating wrongfully convicted inmates through DNA evidence. It has helped clients in the majority of the 198 exonerations nationwide and receives thousands of letters each year from inmates who say DNA testing will prove their innocence. But there is a massive backlog for forensic DNA testing on old cases.

"The concept of an innocence claim after a conviction is incongruous to most people," Mr. Rago said. But if the number of DNA exonerations continues to rise, he said, prisons and judicial systems must prepare for that reality and develop guidelines to accommodate the needs of people who have spent five, 10 or 20 years in penitentiaries, Mr. Rago said.

Currently, the federal government, 21 states and the District of Columbia offer compensation to a prisoner who has been exonerated. Pennsylvania provides nothing.