Criminal cases rise and fall on the strength of the witnesses. The most common people who testify in court are so-called fact witnesses – people who witnessed an event and are called to testify about what they saw or heard. These witnesses include: police officers who stop drivers suspected of drunk driving; women who accuse their spouses of beating them up; and bank tellers who were robbed at work. Fact witnesses who testify in court are first questioned by the attorney who called them to testify, and then cross-examined by the opposing attorney.
- All witnesses are required to be competent to testify. In Massachusetts, a witness is competent when he possesses the mental capacity to: observe and remember events (and then describe those events to the judge or jury); and understand the difference between the truth and a lie. Questions of competency arise most often in the areas of mentally ill witnesses or child witnesses. When an attorney suggests to the judge that a witness might be incompetent, the judge ordinarily conducts a hearing outside the presence of the jury. The judge can independently determine whether the witness is competent, or the judge can order the witness to be examined by a doctor (who will then offer an opinion regarding competence to the judge).
- Of course, even if a witness is competent, his testimony might still be tainted by bias. A police officer doesn’t want to believe he improperly arrested the defendant. A woman claiming to have been beaten by the defendant doesn’t want him to walk free. The bank teller who identified the defendant as the robber doesn’t want to believe she wrongly identified an innocent person. All of these witnesses have biases that may cause them to tailor their testimony to be most helpful to the prosecutor. An experienced criminal defense attorney can effectively cross-examine all witnesses on the existence of bias and, if appropriate, argue to the jury that the witnesses’ testimony should not be believed.
When there is a complex scientific, technical, or otherwise unusual topic that is being discussed in court, lawyers will sometimes call expert witnesses to testify. An expert witness is someone who has specialized knowledge in a particular field and is asked to educate the judge or jury about the subject. Examples of expert witnesses are: a medical examiner who performed the autopsy of the victim in a homicide case; a DNA analyst who studied forensic material left behind at a crime scene; and an experienced drug detective who can offer his perspective about a cryptic exchange of items on a public street that might have constituted a drug deal.
- As with any other witness, expert witnesses are not permitted to offer their opinions about the ultimate issue in the case. Therefore, a medical examiner can offer an opinion that the victim died as a result of a gunshot to the chest, but cannot testify that the defendant is guilty of murder. A drug detective can testify about a drug dealer’s business tools (such as a digital scale and packaging materials), but cannot testify that the defendant sold drugs. Whether the Commonwealth has proven all of the elements of a case is a question for the judge or jury – not any of the witnesses.
- When the Commonwealth is going to call an expert witness to testify, the defense attorney will often hire his own expert to rebut the Commonwealth’s expert’s testimony. It’s not rare for the Commonwealth’s experts to make mistakes that can be identified by a defense expert. Attorney Spring once tried a child rape case where the Commonwealth’s DNA expert failed to notice that the defendant and the alleged victim were related by blood, which caused her to use an incorrect mathematical formula to calculate the DNA results. By hiring his own DNA expert to review the Commonwealth’s expert, Attorney Spring was prepared to cross-examine the Commonwealth’s expert on her error, and she ended up looking foolish in front of the jury. Click here for a partial transcript of Attorney Spring’s cross-examination of two of the Commonwealth’s DNA experts.
Sometimes trial witnesses are called to testify about a defendant’s past conduct, which is not directly related to the current allegations. The prosecutor might call a witness to discuss the defendant’s prior bad acts. A defendant’s prior bad act is not admissible to prove he has a propensity to commit a crime – it is admissible to establish his pattern of conduct. For example, a defendant who uses a distinctive weapon and distinctive mask to rob a bank – and who used the same weapon and the same mask to rob a bank 10 years earlier – might have the facts of the first robbery shared with the jury considering the second robbery in order to establish the defendant’s modus operandi.
In limited circumstances, the defendant may call witnesses to testify about his good character. Character witnesses are permitted to testify about a defendant’s reputation in the community regarding a trait that is the subject of the trial. For example, a defendant charged with assault and battery may call witnesses to testify that he has a reputation in the community for being peaceful. A defendant charged with larceny may call witnesses to testify that he has a reputation in the community for being honest.
Finally, in some criminal cases, evidence is introduced through witnesses who do not appear in front of the jury. Absent witnesses may have their statements introduced through third parties (such as a police officer or an independent witness) if the witnesses are unavailable to testify and their statements constitute exceptions to the prohibition against hearsay. For example, a victim who died of a gunshot wound but identified his killer moments before his death might have his statement introduced at trial as a dying declaration. A woman who was beaten by her husband and frantically shared the facts of the assault with a police dispatcher might have her statement introduced as an excited utterance (even if she asserts her marital privilege and does not testify). Whether the statements of absent witnesses are admissible at trial will be subject to pretrial hearings where the defense attorney will argue to the judge that the Commonwealth should not be permitted to share the evidence with the jury.