I WORKED as a prosecutor for nearly seven years under two Philadelphia district attorneys, followed by a stint under two mayors. I now run a criminal defense and civil rights practice. Much of the district attorney's race has focused on criminal justice reform, including promises to expand diversionary programs, crackdown on unlawful stop and frisk, abolish the cash bail system, lower prison populations, and end or limit the use of the death penalty. On many of these issues the candidates agree.

However, there's another measure of reform that deserves all of the candidates' - and the city's - attention: a commitment to obtain, review and, when pertinent, produce impeachment materials for all law enforcement officers called to testify at trial. This practice would require the district attorney's office to obtain, review and pass to the defense, among other materials, citizen complaints, Internal Affairs reports, and any information contained within the stop-and-frisk database that might reflect on an officer's truthfulness and integrity. A tall order, perhaps, but a necessary one.

Two of the candidates for DA have already weighed in on this issue. At a recent debate, I asked John O'Neill and Joe Khan, former prosecutors, whether internal investigatory materials concerning police witnesses should be made available to assistant district attorneys, as well as to the defense bar and defense attorneys like myself. Both O'Neill and Khan gave a resounding yes. And with good reason.

The role of a prosecutor is to be a seeker of truth, not a collector of convictions.

Prosecutors have a legal and ethical obligation to provide the defendant in a criminal case with exculpatory and impeachment evidence when such evidence is material to guilt or punishment.

This obligation is strictly adhered to and, in some areas, expanded upon in our federal system, particularly with respect to impeachment information concerning law enforcement witnesses. In a Jan. 4, 2010, memo titled "Guidance for Prosecutors Regarding Criminal Discovery," Deputy Attorney General David W. Ogden establishes a federal prosecutor's obligation to obtain information from all members of the prosecution team, which includes law enforcement officers.

This information can include "any finding of misconduct that reflects upon the truthfulness or possible bias of the (officer), including a finding of lack of candor during a criminal . . . proceeding" and "prior findings by a judge that an (officer) has testified untruthfully, made a knowing false statement in writing, engaged in an unlawful search or seizure, illegally obtained a confession, or engaged in other misconduct." This expansive definition allows a prosecutor to determine what information, if any, should be produced to the defense.

This protects prosecutors, police officers, the criminally accused and the integrity of the criminal justice system as a whole. Nonetheless, the Philadelphia district attorney's office does not regularly request impeachment information concerning law enforcement witnesses before prosecutors call them to testify at trial.

In such cases, both the prosecutor and the defense attorney are denied the opportunity to review the officer witness' prior history of misconduct or other information that may reflect on the officer's integrity or truthfulness. While many criminal defense attorneys request and subpoena this material, in the absence of guidelines like the U.S. Attorney's Manual, which reinforce a prosecutor's ethical obligations, such requests are often met with resistance.

This resistance is all the more frustrating in light of the fact that federal prosecutors across the country, and here in Philadelphia, already engage in this practice to protect the integrity of the justice system and the rights of the accused.

In effect, a defendant facing criminal charges at 6th and Market will know the history of the law enforcement officer testifying against him, while a defendant at 13th and Filbert will face that same officer, blindly called by the city prosecutor, without the ability to challenge that officer's credibility with impeachment information.

When a law enforcement officer engages in misconduct or criminal activity, everyone is impacted negatively: from the defendant facing charges or serving a sentence based on the testimony of an officer who may have been untruthful to the prosecutor who called an officer to testify; and the honest, hardworking and dedicated officers who risk their lives, only to have their work tarnished by those who don't live up to the requirements of the badge.

As we get ready to elect our next DA, it is time for Philadelphia to demand a culture of transparency in the district attorney's office with respect to commonwealth witnesses.

Where a culture of transparency prevails, good officers will be protected by their record, and those who violate the tenets of law enforcement will be held accountable; the right to a fair trial will be vindicated; and prosecutors will be able to present their cases with confidence in police witnesses and without fear of surprise.

In the end, the quality of justice should not turn on whether one is charged with a state crime or a federal one.