One the frustrating things about being a defense attorney is the presumption that prosecutors only bring cases when they are sure the defendant is guilty. Unfortunately, prosecutors just do not spend a lot of time pondering whether each individual defendant is guilty. Now an interesting study from earlier this year found that one of the predictive factors in having a case later overturned was the prosecutor having had a weak case. The study compared the overturned convictions with what they called “near misses,” or cases where an innocent defendant was indicted but released before a conviction. (To determine that the near misses were actually innocent, the study examined the evidence to see if the person was actually innocent.) Overall in the near misses, the prosecutors actually had stronger cases. This is counterintuitive as we usually expect weaker cases to be dismissed sooner and stronger cases to have a higher chance of conviction.

To explain this phenomenon, some explanations are more charitable than others. Among the more generous interpretations are that prosecutors, realizing the weakness of their case, prepare for trial better, or that this is merely a failing of the human mind. Prosecutors who indict in spite of a weak case must first convince themselves of the correctness of their position. That internal conviction “translates” well with jury, and the jury convicts because of the confidence of the prosecutor. A less generous interpretation is that prosecutors with weak cases take active measures to illegally withhold evidence from the defendant. They become so committed to proving the defendant’s guilt that evidence potentially exonerating the defendant is discounted. In some of the cases the study examined, the prosecutor failed to turn over exculpatory evidence.

Other possible explanations the study highlighted are that prosecutors might behave differently when they have a weak case. While the police and the prosecutor are still investigating, they often realize they need to shore up weak aspects of their case. In some of the overturned convictions, the prosecutor used a lineup based on a merely passing resemblance to the victim’s description of the perpetrator; some victims feel compelled to select someone out of a lineup, but once a victim chooses someone they are unwilling or unable to tackle the idea they may have made a misidentification. In some cases, the prosecutor used a snitch to provide corroborating testimony. (The word “snitch” has a specific use in terms of testimony. It refers to someone who is not an eyewitness, but that supposedly gets an accused person to confess or corroborate all or part of the case against them. For myriad reasons, such testimony is extremely unreliable. Often, a snitch will receive compensation in the form of a reduced sentence or better living conditions in exchange for testimony. Unfortunately, juries often give snitches too much credence.) These actions have the effect of confirming a prosecutor’s incorrect hunch about a case, and people love when their hunches are confirmed.

This is just one of the many reasons that defense attorneys frequently remind juries to hear all the evidence and evaluate it on its own terms. Prosecutors frequently are wrong, and, as this study suggests, sometimes more likely to obtain a conviction when a case is weaker. That is why juries must actually listen to the evidence presented and uphold their duty to find a defendant guilty only when they are guilty beyond a reasonable doubt.