This is Part 1 of a series. Read Part 2.

The murder case against Tony Bennett seemed pretty straightforward.

Shortly before midnight on May 7, 1994, police found a 26-year-old man in the foyer of an apartment building near Flushing, Queens. Jake Powell was near death, blood pouring from a gunshot wound, but he managed to speak the name of the man who had shot him: "Tony Bennett."

Bennett, a two-time felon, was eventually captured, convicted of murder, and sentenced to 25 years to life in prison.

But Bennett never served anywhere near that sentence. He has, in fact, been free since 2008 because Claude Stuart, the former Queens assistant district attorney who handled his case, violated a basic rule of law by withholding critical evidence from Bennett's attorney. A state appeals court overturned Bennett's conviction and released him after 13 years in prison.

That early release has freed Bennett to describe his role in a crime he had insisted for two decades he did not commit.

"He was wrapped up in a shower curtain in the corner of the bathroom, shivering and shaking," Bennett recalled of Powell, who Bennett said had terrorized his family for years. "He was saying all this, 'Please, please, don't hurt me, don't shoot, I'm sorry, I'm sorry.' And I said, 'Yeah, I'm sorry, too.' And I did what I had to do."

Stuart's wrongdoing in the Bennett case wasn't his only act of misconduct. He manipulated evidence in another case, and that conviction wound up being reversed by the courts, too. But his bosses took no action after that misconduct became known. A state disciplinary committee reprimanded Stuart, but that fact remained secret from the public. Indeed, Stuart's superiors did not act until another conviction was overturned, and Stuart was found to have lied to a trial judge about the whereabouts of a key defense witness.

That, at last, cost Stuart his job.

Stuart's career, across many years and with repeated abuses, helps demonstrate a broader truth: New York's system of attorney oversight is ill-equipped or unwilling to identify, punish and deter prosecutors who abuse their authority.

A ProPublica analysis of more than a decade's worth of state and federal court rulings found more than two dozen instances in which judges explicitly concluded that city prosecutors had committed harmful misconduct. In each instance, these abuses were sufficient to prompt courts to throw out convictions.

Yet the same appellate courts did not routinely refer prosecutors for investigation by the state disciplinary committees charged with policing lawyers. Disciplinary committees, an arm of the appellate courts, almost never took serious action against prosecutors. None of the prosecutors who oversaw cases reversed based on misconduct were disbarred, suspended, or censured except for Stuart. (Stuart declined repeated requests for an interview for this story.)

Nor were any but Stuart punished by their superiors in the city's district attorney offices. In fact, personnel records obtained by ProPublica show, several received promotions and raises soon after courts cited them for abuses.

The damage from prosecutorial misconduct can be devastating, not only allowing guilty people like Bennett to go free, but also putting innocents behind bars. In 10 cases identified by ProPublica, defendants convicted at least in part because of a prosecutor's abuse were ultimately exonerated, often after years in prison.

Shih-Wei Su was incarcerated for 12 years on attempted murder charges before a federal appeals court cleared him, finding that a prosecutor had "knowingly elicited false testimony" in winning a conviction. The city eventually paid Su $3.5 million. The prosecutor received nothing more than a private reprimand.

Jabbar Collins served 15 years in prison for a murder he didn't commit before his conviction was thrown out in 2010; Michael Vecchione, a senior Brooklyn prosecutor, had withheld critical evidence during trial. Collins has filed a $150 million lawsuit against the city. No action has been taken against Vecchione.

Last July, two men filed lawsuits for a combined $240 million against the city for wrongful convictions that a state appeals court found were won in part because Manhattan prosecutors had withheld evidence. The men served 36 years in prison, collectively. The prosecutor, who long ago left the district attorney's office, has not been publicly disciplined.

"It's an insidious system," said Marvin Schechter, a defense attorney and chairman of the criminal justice section of the New York State Bar Association. "Prosecutors engage in misconduct because they know they can get away with it." (Schechter said he was expressing his own opinion, not that of his bar section.)

New York City's district attorneys say concerns about misconduct — heightened by several recent high-profile cases — are largely misplaced.

Allegations of such practices are substantiated in only a fraction of the roughly 285,000 cases they handle each year, they assert. Even in those, they add, what courts deem misconduct often amounts to inadvertent error.

Top prosecutors also say their offices have taken significant steps to limit and expose misconduct, in part by establishing internal units that examine claims of abuse.

"The egregious cases don't mirror the larger universe, but are rather somewhat isolated," said John O'Mara, head of the Brooklyn District Attorney's Conviction Integrity Unit.

There have been a variety of reports over the years, both national and local, that documented a substantial array of serious misconduct involving front-line and senior prosecutors alike.

Across those years, there has been at least one constant: the inability or unwillingness to meaningfully punish the offending prosecutors.

ProPublica, in the latest analysis, examined the years 2001 to 2011, chiefly scrutinizing instances in which state or federal courts identified misconduct serious enough to throw out a conviction. The analysis also incorporated civil cases during those years, virtually all of which resulted in financial awards being given to the victims of such misconduct.

The analysis found a total of 30 cases that met those criteria. Four of them involved civil cases addressing harmful misconduct that took place as far back as 1985. Again, in all those cases, no prosecutor other than Stuart was seriously disciplined for misconduct.

Calculating the full extent and impact of prosecutorial misconduct can be difficult. More than 90 percent of criminal cases never go to trial, so the public has no way of knowing how prosecutors conduct themselves in the tens of thousands of cases every year that, for instance, end in plea deals.

Moreover, state appellate courts — in theory the first check on misconduct allegations — often criticize prosecutorial tactics but let convictions stand if they conclude the conduct did not decide the outcome of the case.

ProPublica identified more than 50 instances in which appeals courts essentially gave prosecutors such no-harm, no-foul free passes. In a 2009 ruling, for example, a court found that a Manhattan prosecutor should have disclosed a co-conspirator's statement that the defendant wasn't actually involved in the shooting he was charged with, but concluded there was "no reasonable possibility that the failure to disclose … contributed to the verdict."

Academics and defense lawyers say such rulings allow prosecutors to engage in bad practices as long as they don't result in unjust convictions.

"If you're in the Olympics and you're in a race and you win and then it's found that you took steroids, they take your medal away," said Larry Goldman, a former Manhattan prosecutor who is now a defense attorney. "No one says, ‘Oh well, it doesn't matter if you took steroids, you would've won anyway.'"

When courts and grievance committees shrug off problematic conduct, Goldman and others said, they miss opportunities to deter more misconduct before it worsens, often disastrously.

When prosecutorial misconduct goes unchecked, said Hal Lieberman, a former chief counsel for a New York grievance committee, it "undermines the integrity of the entire system."

* * *

Stuart was assigned the Bennett case as he neared his 10-year anniversary with the Queens District Attorney's office, soon after being promoted to the Career Criminal Major Crimes Bureau.

Stuart had Powell's final words identifying his killer, and he notified Bennett's lawyer that those words would be the key to his prosecution.

But on the last day of the trial, Stuart produced a surprise witness: a man who testified that he, too, had heard Powell identify his killer.

The jury returned a guilty verdict.

Looking back, Bennett said, Stuart had "pulled a rabbit out of his hat."

A state appellate court took a dimmer view, finding that Stuart had "ambushed the defense by his deception."

The court overturned Bennett's conviction. Bennett, after pleading guilty to a lesser charge, was soon free.

Prosecutors' obligation to disclose potentially important evidence to defense lawyers is a bedrock principle of the justice system. Under the U.S. Supreme Court's 1963 Brady v. Maryland decision, prosecutors must disclose any evidence that is material to either the guilt of the defendant or the severity of the alleged crime. Under New York state court ruling People v. Rosario, New York prosecutors must turn over statements by witnesses who will give testimony.

But ProPublica's analysis showed that violations of these obligations were the most common form of serious misconduct by city prosecutors, who failed to meet these standards in more than half of the 30 cases reversed by state or federal courts based on misconduct.

Prosecutors said Brady and Rosario violations are almost always accidental and sometimes involve complex judgment calls about what evidence needs to be turned over and when.

"The decision as to what constitutes material that must be disclosed under Brady is not always simple to make and often subject to debate," John Ryan, the chief assistant district attorney in Queens, said in a letter to ProPublica. The case law governing Brady is always changing, he added, and sometimes even appellate judges disagree on what is required.

Dozens of current and former prosecutors told ProPublica they received vigorous training on how to make decisions on Brady, worked closely during trials with supervisors, and were urged to err on the side of disclosure.

But Schechter, the head of the criminal section of the state bar, has said the culture and training in the offices of prosecutors may sometimes lead prosecutors to skirt the rules in their desire to win victories in court.

"Assistant district attorneys do not emerge from law school with a genetic disposition to hiding Brady material," he wrote in a July 2012 letter to the bar association published in the New York Criminal Law newsletter. "Instead this is something which is learned and taught."

The letter triggered an explosive reaction: Bronx District Attorney Robert Johnson called Schechter's allegations "outrageous," and Schechter's own bar association section passed a resolution disowning his statements.

Yet a number of former prosecutors have made similar observations.

Mortimer Lawrence, Claude Stuart's former colleague at the Queens district attorney's office, testified at a disciplinary hearing for Stuart that supervisors bore some responsibility for Stuart's troubles.

"I know there to be an unspoken pressure on assistants to press the edges of discovery and evidence and just how far you go," Lawrence said in his testimony.

Stuart lost his job in 2002 and had his license to practice law suspended in 2005.

Ryan, the Queens chief assistant district attorney, stressed that once Stuart's supervisors knew of his misconduct, they moved swiftly to alert disciplinary authorities.

To critics, however, Stuart's pattern of abuses shows how much a prosecutor can bend the rules before suffering any consequences.

Over the course of his career, Stuart's tactics prompted appellate courts to toss two other convictions in addition to Bennett's and forced his superiors to abandon at least one other case, records show. He also had received a private letter of caution from a disciplinary committee related to one of the reversals, although his bosses say they were not aware of this.

Yet, until Stuart's forced resignation, there were no signs that Queens District Attorney Richard Brown saw him as a problem. Instead, Stuart had garnered a string of raises, promotions, and positive performance reviews, winning a reputation as an aggressive litigator, according to records and interviews.

"We have a broken system," said New York University legal ethics professor Stephen Gillers. "We disbar lawyers for taking two hundred dollars from a client's escrow account, even if they return it. But there are rarely consequences for someone who has stolen someone else's due-process rights and possibly put an innocent person in jail."

* * *

In the early 1990s, parts of Queens were plagued by Chinese gang violence. There were the White Tigers and the Green Dragons, grudges and guns.

In 1992 prosecutors charged Shih-Wei Su with ordering the attempted executions of two Green Dragons in a Bayside pool hall.

The star witness for the prosecution was man named Jeffrey Tom. Tom had agreed to testify that he heard Su order the shootings in exchange for prosecutors scaling back a criminal case against him.

But at trial, under questioning by Queens Assistant District Attorney Linda Rosero, Tom denied any deal with prosecutors existed. Rosero let the lie stand and then, in summation, lauded Tom's testimony as "truthful and honest."

Su, 19 at the time of his conviction, was sentenced to 16 to 50 years in prison.

It would take years, but the conviction did not survive. Su's lawyers successfully proved a deal had existed, and in 2003 a federal court overturned the outcome. The judges savaged Rosero, calling her conduct "repugnant to the Constitution."

Su filed a wrongful-conviction suit against the city, but he wanted Rosero punished, too. With the help of his attorney, Joel Rudin, he lodged a disciplinary complaint with the Second Department Grievance Committee. Rudin shared the correspondence with ProPublica.

To trigger investigations against prosecutors, grievance committees depend largely on reports from defense attorneys, who may be reluctant to come forward and antagonize a prosecutor with whom they must continue to work.

ProPublica interviewed eight current or former disciplinary committee officials, who said they recalled very few complaints filed about prosecutors.

The committees operate almost entirely in secret, dispensing little public discipline—disbarments, censures, or suspensions. Between 2001 and 2009 (the latest year for which data are available), just 1 percent of the roughly 91,000 complaints received by the First and Second Department committees resulted in public sanctions. And just 5 percent of all the complaints resulted in even so much as private letters of caution or admonition, which remain confidential to all but complainants and the attorneys who receive them.

Though prosecutors are public employees, members of the public have virtually no way to find out if they have been sanctioned privately or why.

Ellen Yaroshefsky, a Cardozo Law School professor, has tried for years to obtain records of complaints and disciplinary actions against New York prosecutors. The disciplinary committees have refused to comply, citing confidentiality laws.

Richard D. Willstatter, former president of the New York State Association of Criminal Defense Lawyers, argues that prosecutorial oversight should be more transparent.

"We understand the need to protect attorneys from scurrilous complaints, of course, but we don't think these rules should apply to public officials like judges or prosecutors," Willstatter said. "If the information is brought to the attention of the public, then it is more likely that there will be pressure to make the system fairer."

To critics like Yaroshefsky and Willstatter, private discipline can be a grossly inadequate way to hold prosecutors accountable.

Certainly, Su's bid to have Rosero punished fizzled.

As part of the disciplinary process, Rosero claimed her supervisors pressured her into trying a case "thought to be a loser." Still, she insisted her handling of the witness testimony was an innocent mistake, not gamesmanship to score a win.

Rosero, who has left the Queens District Attorney's office, declined to comment about the Su case. In a letter to the grievance committee, her attorney, Jerome Karp, said that Rosero, who had been with the Queens District Attorney's office for five years when she tried Su, had been "naïve, inexperienced and, possibly, stupid."

In December 2004, the grievance committee decided to issue Rosero a confidential letter of admonition. Publicly, Rosero's record remained unsullied.

Su would not relent. While there is no formal appeals process for disciplinary decisions, nevertheless Su wrote back to beg the committee to reconsider: "How is it possible that an experienced prosecutor who knowingly broke every bar association code, every Constitutional law, and more, only gets an admonition?" he asked.

The committee was unmoved.

"The matter," it told Su in a letter, "is closed."

* * *

Queens Assistant District Attorney Elizabeth Loconsolo was a rising star when, in October 1989, she began work on what appeared to be a horrific case of child abuse. Amine Baba-Ali, a 33-year-old Algerian man, had been charged with raping his 4-year-old daughter in the midst of a nasty divorce with the girl's mother.

Loconsolo had recently won several high-profile rape cases, including one against a man known as the "duct tape rapist" for his use of the material in assaulting eight young girls.

Critical to the Baba-Ali case were medical evaluations done on the child. One examination, done less than a week after the alleged rape, showed no indication of physical harm. Another, done more than three months after the alleged assault, supposedly showed evidence of rape.

Loconsolo used the damning examination results at trial. But she didn't turn the potentially exonerating results over to Baba-Ali's lawyers until the eve of his trial. His lawyers never used the material in his defense.

Baba-Ali was convicted of rape and sodomy and sentenced to up to 25 years in a maximum-security prison.

Less than a month after the conviction, Loconsolo was given one of the biggest pay raises of her 10-year career and eventually rose to head the office's Major Offenses Bureau, the first woman to hold the post.

Two years later, Loconsolo's victory was thrown out by a state appellate court. The court ruled that Loconsolo's handling of the exculpatory medical records was "inexcusable" and a violation of a direct court order.

Baba-Ali was freed in January 1992. Loconsolo, despite the stinging rebuke, got another raise later that year.

Loconsolo's career underscores a question that has frustrated defense lawyers and legal experts for years: Why don't district attorneys reliably punish assistants under their command?

Senior prosecutors across the city insist they have reprimanded subordinates whose actions have resulted in wrongful convictions and have used such cases to guide how all staffers are trained.

But ProPublica's review of personnel records for assistant district attorneys involved in the 30 harmful misconduct cases showed that none of the prosecutors were dismissed, demoted, or sanctioned in any formal way except for Claude Stuart. (We have not received personnel records for prosecutors involved in three of the cases.)

The records were often incomplete, but at least seven of the prosecutors received raises or promotions after convictions were reversed.

Joel Rudin, the lawyer who handled Su's civil suit and who now represents Jabbar Collins, found a similar pattern in older personnel records obtained from Queens and the Bronx as part of litigation on behalf of defendants who were wrongfully convicted.

In a 2011 article for the Fordham Law Review, Rudin wrote that just one Bronx prosecutor found to have committed misconduct by appellate courts in 72 cases from 1975 through 1996 was even briefly disciplined by his superiors.

The same prosecutor was blasted in three more appellate opinions over the next three years for conduct described as "egregious," "outrageous and abusive," and "improper and tasteless," Rudin found.

None of the Queens prosecutors who handled 73 cases reversed by appellate courts between 1985 and 1998 based on misconduct even received a negative performance evaluation, Rudin found.

In most of the 30 reversals examined by ProPublica, where courts cited prosecutors for harmful abuses, city district attorneys maintain that no abuses occurred, only mistakes.

Of the 12 cases involving Queens prosecutors, Queens Chief Assistant District Attorney John Ryan said the only ones involving bona fide misconduct were those handled by Stuart. The others were either inadvertent errors, the fault of police, or "simple disagreements over the requirements of the law" between prosecutors and the court, he said.

In the eyes of Manhattan prosecutors, none of the six Manhattan reversals involved true misconduct, Chief Assistant District Attorney Daniel Alonso said.

"Some judges opined that a prosecutor had acted improperly, while others disagreed," Alonso said in an email to ProPublica. "This is the nature of criminal litigation, and it happens with respect to defense lawyers and judges as well as prosecutors, the overwhelming majority of whom are simply making judgment calls in good faith."

The judges in Baba-Ali's case could hardly have been more emphatic about Loconsolo's misconduct and its consequences. And it was not the only time she would have her work criticized. In October 1992, she had another child abuse conviction reversed by a federal judge, who found "troubling issues" with the prosecution.

As far as her personnel records show, however, Loconsolo was never formally reprimanded by her bosses. She stayed in the Queens office, got another raise, and was assigned to head what was known as the intake bureau, where she would oversee and train young front-line prosecutors making sensitive judgment calls on how to handle new arrests.

Baba-Ali, released from prison after two years, wanted compensation for the years he'd lost and the horrors he'd experienced in prison. He filed a complaint with the state court of claims, saying that when he was incarcerated, mostly at Sing-Sing correctional facility, he was beaten and had witnessed, among other things, a young inmate serially gang-raped as guards looked on. Perhaps most damaging, Baba-Ali claimed, the case had left him permanently estranged from his daughter.

State Court of Claims Judge Melvin Schweitzer didn't spare Loconsolo. He said what she did was "tantamount to fraud" and awarded Baba-Ali $2.1 million — an award the state is still contesting to this day. Last June the State Court of Appeals sent the case back to the court of claims for retrial.

In a letter to ProPublica, Ryan said Loconsolo "has maintained for the last twenty years that she disclosed the records in a timely manner" and there was no reason to take any action against her.

Loconsolo, who didn't respond to requests to be interviewed for this article, seems to have done just fine.

She's now general counsel for the Nassau County Sherriff's Department.

"You just can't expect the district attorneys to hold their own people accountable for wrongdoing," said Hugh Mo, a former New York Police Department deputy commissioner and Manhattan prosecutor who is now in private practice. "It's a serious conflict of interest."

* * *

Prosecutorial misconduct, and how to deal with it, is not a new legal topic. For years, defense attorneys and prosecutors have debated ways to keep prosecutors in line and discipline them when they err.

In the last few years, the New York State Bar Association has taken on the issue of how to define prosecutorial misconduct and what should be done about it as part of a larger initiative to address wrongful convictions.

In a 2009 report, the group made several recommendations aimed at stiffening oversight of prosecutors and stamping out problems with evidence disclosure.

New York lawmakers have introduced several bills incorporating the bar association's ideas. Some are pending this session, but none have gained much traction. The District Attorneys Association of the State of New York has opposed them, and city district attorneys have said they could adversely affect public safety and are unnecessary in light of their own efforts to improve training and oversight.

There is ample skepticism among defense lawyers and other legal experts that any reforms will prevail.

A former grievance committee member, who declined to be named because of his ongoing work with the courts, said the state's most senior judges could take the lead and make something happen.

"I think the presiding justices would have to recognize the seriousness of the situation and take the initiative and say, ‘Listen, from now on, when you identify an act of misconduct, you have to open up an investigation,'" he said.

Prosecutors in Manhattan and Brooklyn say they have moved voluntarily to accomplish some of what the proposed legislation would have mandated.

The offices have set up conviction integrity units to review cases in which there is compelling evidence of innocence. The Brooklyn unit has assessed 14 cases and exonerated three defendants since it was established two years ago. Manhattan would not provide details about its unit.

In October 2009, the Brooklyn office created an internal ethics panel to investigate allegations of misconduct made against its attorneys. Based on the panel's work, Brooklyn officials said, two attorneys have been asked to resign. Another resigned in May while the ethics panel was investigating her conduct in a rape case.

John O'Mara, who leads the Brooklyn Conviction Integrity Unit, said these steps make outside intervention unnecessary.

"We are comfortable with our current system," O'Mara said.

Outside observers are less certain.

"You can't have a system where everybody that has the ability to do something about a problem is saying ‘it's not my responsibility,'" said professor Steven Goldblatt, a former prosecutor who is now director of the Appellate Litigation Program at the Georgetown Law Center. "There is a public trust at stake here."

Aarti Shahani and Melanie Hicken contributed to this report.

Live chat: What is being done to improve oversight in these cases? Join reporter Joaquin Sapien and a team of legal experts this Thursday at noon ET to discuss our latest investigation into prosecutorial misconduct. You can also tweet questions with #PolicingProsecutors.