A defendant's right to a fair trial imposes important limitations on how prosecutors can characterize evidence or argue their case before the jury. If a prosecutor makes objectionable comments during trial, the court has wide discretion whether to let the comment slide or declare a mistrial and force the State to start its case over in front of a new jury. However, if a prosecutor repeatedly makes inflammatory or misleading comments, the cumulative effects of those statements may require the defendant to receive a new trial.
An example of this can be seen in a recent case out of the Miami-Dade area, Moreno v. State. In Moreno, the defendant was arrested after performing poorly on field sobriety exercises after he was pulled over, but his blood alcohol content was never measured. His defense at trial was that he was not drunk, but that his driving and performance on the field sobriety exercises were caused by a dental procedure.
At trial, the prosecutor elicited testimony that made the field sobriety exercises appear more reliable than they were by referring to them as "tests" and using terms like "indicators" and referring to the defendant's results as "not to standard". A prior case, State v. Meador, criticized the reliability of field sobriety exercises and observed that there was no numerical correlation between performance on these exercises and a person's blood alcohol content.
The court in Moreno found that the State's characterization of the evidence was improper, but found that a mistrial was not necessary. It noted that most jury members incorrectly assume that field sobriety exercises are scientifically accurate, and that the State's mischaracterization of the evidence was not of great significance.
However, during closing argument, the prosecutor went on to criticize the defense case by stating that the defendant "kept evidence" from the jury and "passed up an opportunity to provide a breath sample to show he hasn't been drinking." The court once again sustained objections for these comments but denied a mistrial. However, the appellate court reversed, finding that the cumulative effect of these comments denied the defendant a fair trial. Specifically, the prosecutor created the impression that the defendant had the burden to prove his case, rather than the State.
Results like the Moreno decision show that how evidence is characterized in a DUI trial can be just as important as which pieces of evidence are admitted. Even relatively minor misstatements of the evidence may add up to a mistrial if the prosecutor continues to mislead the jury.