A U.S. Supreme Court ruling in 1963 required prosecutors to hand over to the defense evidence they uncover, even if it is exculpatory (meaning it could potentially help the defendant). Despite the fact that this is required in criminal defense cases across the country, in practice prosecutors do not always comply with this ruling. Texas is among the states that have adopted "open file" reforms to address this issue.
One of the biggest challenges about requiring prosecutors to disclose exculpatory evidence is that the prosecutors are ultimately the ones deciding what is considered evidence. This is a subjective decision made by the defendant's opponent. Critics say that depending on self-enforcement is not always adequate, and there certainly have been cases where defendants have been sentenced without a fair trial due to withheld information.
Texas is one of the states that has taken steps to prevent this. Along with Ohio and North Carolina, the state is one of very few to have passed open-file reforms. This requires all law enforcement agencies to hand over files to both the prosecution and defense so that both sides have the opportunity to examine all evidence and determine relevance.
Other states are attempting to pass similar laws but have received push back from police unions. Officers in some states worry that their privacy and reputations will be on the line should everything be disclosed. Criminal defense advocates, however, feel that the move is necessary to stop innocent people from going to prison. Those who are accused of a crime in Texas should speak with a lawyer about how the state's open-file laws can help support their case.
Source: governing.com, "More States Forcing Prosecutors to Hand Over Evidence -- Even When It Hurts Their Case", J. Brian Charles, April 20, 2018