But that's not always how it works.
Despite the legal requirement to turn over exculpatory evidence, prosecutors sometimes sit on material they've collected, or they may not actively look for such evidence. Law enforcement agencies may not willingly provide it.
“The problem with Brady is it’s pretty much self enforcing," says Nina Morrison, senior staff attorney with the Innocence Project. "It’s a subjective judgment, and you are asking prosecutors who are competitive to do something that can harm their chances to win a case.”
And the self enforcement of the rule has too often, in the eyes of judges, defense attorneys and some prosecutors, had disastrous results.
In California, statements from a jailhouse informant were not disclosed to the defense attorneys in a case where a teenager was being charged with attempted murder. He would spend two years in jail awaiting trial before the charges against him were dismissed.
Prosecutors in New York City withheld evidence in the 2010 murder conviction of Wayne Martin. A doctored police report had erased statements by an eyewitness who told police Martin had not committed the crime. A second report, containing the witness statements was never given to the defense.
The late Ted Stevens, a senator from Alaska, was convicted of federal ethics violations in 2008. A year later it was learned that the U.S. Department of Justice failed to hand over exculpatory evidence in the case. U.S. District Court Judge Emmet Sullivan, who presided over the case, said of the case:
“In nearly 25 years on the bench, I’ve never seen anything approaching the mishandling and misconduct that I’ve seen in this case.”
Now, a small but growing number of states have taken steps to clarify and strengthen the Brady rule requiring disclosure of potential exculpatory material. New York is the latest state to amend its enforcement of the requirement, thanks to a ruling from the state's highest court late last year.
Starting in January, judges in New York have begun instructing prosecutors of their obligation not only to turn over materials that may be favorable to the defense, but to seek that information from law enforcement. Prosecutors must disclose such evidence at least 30 days prior to trial, to give defense attorneys enough time to review the material.
Prosecutors who fail to comply can be censured in the form of a public reprimand by a judge.
“The idea was having something that tells them what they have to do in every single case and when they have to do it by,” Morrison says.
The Innocence Project advocated for the change in New York and is working with other states on similar measures, although it declined to say which ones.
Criminal justice advocates say strengthening Brady rules is a key part of criminal justice reform. Since 2004, Ohio, North Carolina and Texas have all adopted so-called "open-file" reforms, under which all the files of law enforcement agencies, felony investigators and prosecutors are open to examination by both the prosecution and the defense.
New York hasn’t gone that far: The state still maintains a discovery process that, unless the material or evidence is exculpatory, allows prosecutors to hold police statements and witness lists until a jury is selected.
Where Brady rules continue to run into obstacles is in obtaining and making police personnel records available to the defense. When the records are available, defense attorneys will often use police personnel files -- which can contain discplinary write-ups or details about an officer's actions during an investigation -- to attack the credibility of an officer and the veracity of the police investigation.
Police unions have pushed back against disclosing personnel files under Brady to protect officer privacy, but also to keep officers from being labeled "Brady cops," a moniker that can mark them as unreliable in court and jeopardize an officer's career.
“Law enforcement agencies fight us every time. A cop’s criminal conviction can be easy to get into the record. But a bad act in their file is tougher to get into the court record,” says Todd Oppenheim, a Baltimore city public defender. "We will make a request, and the police union will immediately file a protective order."
Efforts at the federal level to reform Brady haven't been successful. Legislation in Congress, introduced by Alaska Sen. Lisa Murkowski in 2012, would have forced federal prosecutors to be more forthcoming with evidence favorable to the defense. But the bill died.
These kinds of requirements are necessary, criminal justice reformers say, because the Brady rule has been applied so inconsistently. Since it leaves disclosure of evidence somewhat up to prosecutors' discretion, it hasn't achieved what the Supreme Court set out to require.
“Brady in practice has fallen far short of its promise,” says John Schoeffel, head of training for the Legal Aid Society. “Whether prosecutors are going to be diligent about finding [evidence] and turning it over is something the defense has no authority over.”
This can lead to wrongful convictions in some cases.
For instance, New York courts since 1989 have overturned 88 cases in which defendants were convicted despite evidence that would have exonerated the suspects.
But more often, plea agreements can be reached and sentences leveled against a defendant without attorneys and the court seeing critical information.
Such was the case with John Leo Brady, a Maryland man who in 1958 accompanied another individual, Donald Boblit, during a homicide. Brady had participated in an auto theft with Boblit on the day of the homicide, but did not participate in the murder. Boblit said as much in a written statement. However, when the men were tried separately, Brady’s attorneys were not made aware of Boblit’s statement.
Brady's case was appealed to the U.S. Supreme Court, which in 1963 ruled that prosecutors must turn over potential exculpatory evidence, even if it may hurt their case.
“Society wins not only when the guilty are convicted, but when criminal trials are fair,” wrote Associate Justice William O. Douglas in favor of the majority.
Since January, the Legal Aid Society has trained more than 500 attorneys in New York on what is and what isn’t Brady material, Schoeffel says. There isn’t data measuring how effective the new rule has been in the courts. However, Brady materials were responsible for nearly 40 percent of the state's exonerated cases since 1989, according to the National Registry of Exonerations.
Prosecutors say the new court rules are too strict and would unfairly punish them for failing to turn over evidence they may not even believe is exculpatory. Additionally, they say, Brady disclosures in some cases may jeopardize the lives of witnesses, which are already often in danger. In Washington, D.C. and Maryland, 37 witnesses were killed between 2004 and 2015, according to analysis by the Washington Post.
"In any case where there is a whiff of violence, cops and prosecutors believe there is going to be retaliation against a witness," Oppenheim says. "But courts should not be unilaterrally claiming that witness information is protected and keeping it away from the defense."
Judges and law enforcment, Oppenheim adds, have the ability to protect a witness from retaliation and still disclose the witness' information to the defense.
At least one high-profile prosecutor, Manhattan District Attorney Cyrus Vance, supports the new court rules.
“I can’t see any reason to object to an order that requires us to do something the law already requires us to do,” Vance told The New York Times.
