Prosecutors have an ethical duty to see that justice is done, not to win convictions at trial. Prosecutors also have a legal duty to hand over any exculpatory evidence to the defense. The problem with Brady material is that the state has it and the defense doesn't. And given the imperfect information defense attorneys deal with in preparing for trial, if you don't know about it (or have an inkling about it), it may as well not exist.
When it was his turn to speak, [Shannon] Edmonds applauded [Stacey] Soule’s findings. “Having information like this is great,” he told the committee, in part because when it comes to prosecutorial misconduct (and ineffective assistance), there is often “more heat than light.” A lot of people “bang the tables about these problems and claim they are epidemic. And those claims don’t always hold up to scrutiny.” If you search online for “prosecutorial misconduct,” he said, you’ll find a lot of complaints and “supposed data that is rarely independently scrutinized” the way Soule had done.As Ms. Smith points out in her article, the problem with using an analysis of Court of Criminal Appeals opinions as the basis for your thesis is that most instances of prosectutorial misconduct don't make it up the chain for a variety of reasons.
The first, and most important, is that some 95% of criminal cases end in plea deals in which the defendant waives his right to appeal in exchange for the promised sentence. In most counties in Texas, at the time of the plea, the defense attorney and the client are both required to sign a document indicating that they received all the discovery they were entitled to and and that the state is under no further obligation to provide discovery material on that case in the future.
While defense attorneys have access to the state's file in criminal prosecutions in Harris County, we have no way of knowing what's not in the file. In some cases potentially exculpatory evidence is "covered" under the work product privilege. In others, it's simply not disclosed because the prosecutor doesn't deem it to be exculpatory.
In general, once the light has been shown on a systemic issue - either by the press or at trial - that information is conveyed to defense attorneys who are advised to contact their clients and proceed as they choose.
The problem is, the state knew about the issue while the case was pending but chose to say nothing and to disclose nothing so they didn't lose their edge.
Ultimately the only way to bring these matters to light may be taking every case to trial and shining a light on the ways in which prosecutors, police and crime labs gather and process evidence. But that "solution" is certainly a non-starter because many defendants don't want to chance a longer or more severe sentence at trial. Some defendants decide to plead because the financial burden of fighting a case is too much for them. Some give up the ghost because the state has allowed courts to pile so many pre-trial bond conditions on them that they'd rather get credit for it by pleading to probation.
If there is no one in the forest, does the falling tree make a sound? Likewise, has the law been violated if the state chooses not to disclose exculpatory evidence when no one else knows its exists? On the one hand, the answer is clearly yes. But, on the other hand, if you can't prove it existed what are you going to do about it?