Criminal Trial - Admissible Evidence

The judge's screening function. To understand criminal trials, it is necessary to understand the role of the trial judge in the admission of evidence. In the Anglo-American trial system the judge performs a screening function for the jury, making sure that the evidence brought before it is relevant and that it is not prejudicial to the defendant or to the state. Many items of evidence that are relevant in a broad sense are kept from the jury because the trial judge has decided that the danger of prejudice to the defendant outweighs the probative value of the piece of evidence in showing that the defendant committed the crime in question. Thus in a murder case, evidence offered by the prosecution showing past arrests of the defendant for assault will not be admitted, nor will evidence of the defendant's reputation as a violent person be admitted as part of the prosecution's direct case. Even gruesome pictures of the body of a murder victim that show the wounds may not be admitted for the jury's inspection if a trial judge feels that the pictures may inflame the jury and distract it from its job of carefully evaluating the evidence in the case. Of course, most evidentiary rulings can only be understood in context, taking into account the other evidence in the case and the legal and factual issues being contested. But it should be apparent that many major battles at a trial may take place outside the hearing of the jury because of the judge's obligation to rule on the admissibility of evidence. Thus one who observes a trial frequently sees the lawyers and the judge conferring at the side of the judge's bench in whispers discussing the admissibility of a piece of evidence or the propriety of a line of questions. Normally, judges try to resolve these questions quickly so they do not have to remove the jury from the courtroom and the trial can continue without a long interruption. Hence the convenience of arguing some evidentiary issues at the side of the judge's bench (so-called sidebar conferences). But sometimes the issue is too complicated or too important to be argued in that abbreviated way and the judge will order the jury to return to the jury assembly room so that a full discussion of the issue can take place in the courtroom. Often a substantial part of a trial is consumed by arguments on evidentiary and other legal issues outside of the hearing of the jury.

Hearsay evidence. Besides the general screening function performed by the trial judge in making sure that the probative value of an item of physical evidence or a line of questioning outweighs any prejudice to the defendant, there are many specific rules of evidence designed to enhance the reliability of trial verdicts. One rule that is central to the Anglo-American system of trials—both civil and criminal—is the rule that bars hearsay testimony.

A hearsay statement is defined as an out-of-court statement offered for the truth of the matter asserted. This rule is perhaps best understood by considering an example. Imagine a bank robbery trial in a case investigated by Federal Bureau of Investigation agent Mary Smith. At the trial of John Doe, the government calls Smith, who proceeds to tell the whole story of the robbery as she learned it from the witnesses. She explains that a bank teller, Johnson, described the robber and picked out Doe in a lineup; she testifies that a bank customer, King, said that the robber wore a green plaid suit and a red bow tie with white polka dots. Finally, Agent Smith testifies that she interviewed Doe's ex-girlfriend and that the girlfriend said Doe owned a green plaid suit and a red bow tie with white polka dots.

All of this evidence as testified to by Agent Smith would be hearsay evidence—it is a series of statements that were made out of court to Agent Smith, and they are being offered for their truth. The problem with such hearsay is that the jury hears only Agent Smith, when the crucial witnesses who should be examined in the jury's presence are the bank teller, the bank customer, and the ex-girlfriend. Because hearsay testimony is inadmissible unless it fits within a recognized exception, the government in this example cannot present its case through secondhand reports of what others said. Instead the prosecution must call the actual witnesses to testify to exactly what they observed and what they each know personally. The jury will then be in a better position to assess the credibility of the witnesses, especially when it is considered that the defense will have an opportunity to cross-examine each of the witnesses and to expose any weaknesses in their testimony.

The ban on the use of hearsay testimony is not absolute. There are many exceptions that would allow it, and, like rules of evidence in general, these exceptions vary from jurisdiction to jurisdiction. One common exception is the rule that permits the admission of a witness's prior testimony if he or she is unavailable. Thus, where a witness testified at the first trial of defendant Doe and there was a hung jury necessitating a second trial, the testimony of this witness could be introduced at the second trial under the hearsay exception if the witness had died before the second trial.