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Either party may use an expert witness in a criminal defense case. As the defendant seeking to admit a criminal expert, you must show that the testimony is needed and that the expert is credible. You may object to the state offering an expert witness and question their credibility. The use of expert witnesses is within the court’s discretion, falling under S.C. Rules of Evidence Rule 702.
Types of Expert Witnesses in Criminal Defense
Forensic Toxicologist
A forensic toxicologist might testify to the impact of alcohol or drugs on a person’s impairment. They might talk about alcohol or drug metabolization in the body in reference to chemical testing. Forensic toxicology may be appropriate to discuss which chemicals were in a person’s system at the time of their death.
Ballistics, weapons
Gunshot trajectory, gunshot residue, and other expert testimony may explain firearm use. Ballistics may explain which gun was used, how many times it was fired, and from what angles. It may be relevant to determine if a person acted in self-defense, or it may explain whether a person was murdered or died from a self-inflicted wound.
Forensic Accountant
A forensic accountant may be important for a crime involving financial fraud. Forensic accountants perform detailed audits and investigations to document financial activity. These experts understand accounting, auditing, and reporting standards; they compile and analyze financial transactions.
Medical, mental health
A medical expert may explain someone’s cause of death. A mental health professional may discuss if someone is competent to stand trial. A medical expert may have conducted an examination, or they may review records to form an opinion.
Science, engineering
Science and engineering experts may be important in a criminal defense case in several ways. An expert may enhance a sound recording for clarity or analyze a handwriting sample. DNA testing or fingerprint analysis may identify a suspect or victim. Testing may identify a type of drug involved. Engineers can examine a cell phone or computer; they may explain cell phone tracking to follow a person’s movements.
Expert Witness Influence, Challenges, and Limitations
The standard for expert witnesses is given in S.C. Rules of Evidence Rule 702. An expert may testify if scientific, technical, or other specialized knowledge will assist the jury. The testimony must help the jury understand evidence or determine a contested fact.
Using expert witnesses can create some challenges and limitations:
- Admission of expert testimony is within the discretion of the court. The defense must be confident that their expert will be allowed to testify based on South Carolina standards for admissibility.
- An expert may testify to an opinion or inference made based on facts or data not admissible in evidence. This can seemingly create a backdoor exception to hearsay and other gatekeepers of evidentiary credibility.
- Pretrial procedures must be complied with for the disclosure of expert testimony.
- Expert testimony can state an opinion of ultimate issue to be decided by the trier of fact. This testimony can be especially powerful; careful cross-examination must be prepared, and a counter-expert should be strongly considered.
An expert witness can be a powerful testimony that heavily influences a jury; a criminal defendant must prepare accordingly.
Who can be an expert witness?
To be an expert witness, a person must be specially qualified by their:
- Knowledge
- Skill
- Experience
- Training
- Education
A person doesn’t necessarily need to have the highest degree possible in the field. They may not even have a degree, but they must have specialized knowledge beyond that of an ordinary person.
Cross-Examination of Expert Witnesses
When cross examining the prosecution’s expert, you want to discredit their opinion. This can be done by critiquing their credibility or methodology. In cross examination, you can ask leading questions.
Effective questioning may involve going in-depth with scientific information. It may mean preparing pointed questions that can vary based on what is ultimately offered in court. Preparing for effective cross-examination begins long in advance of the trial.
How Courts Determine the Admissibility of Expert Testimony
As a defendant, you may object to a prosecution expert. If the court overrules your objection, you may still challenge the person’s credibility and the basis for their opinion.
South Carolina has not adopted the federal Daubert standard, but the test to determine the admissibility of expert testimony is similar. The court may consider:
- Scientific methodology
- Peer review
- General acceptance
- Rate of error of a particular technique
To be admissible, the evidence must be reliable, helpful and relevant. Probative value must outweigh prejudicial effect. See State v. White, 642 S.E.2d 607 (S.C. Ct. App. 2007).
The jury decides how to weigh expert testimony. They may completely disregard it, or they may accept all of the testimony or compare it to other evidence.
On appeal, a conviction may be overturned if the court admitted a prosecutorial expert in an abuse of discretion. State v. Myers, 359 S.C. 40 (2004).
Contact an Attorney
If you are facing a criminal defense case, expert testimony may play a critical role. At Shealey Law Firm, our representation includes preparing for expert witnesses.
To talk about the role of expert witnesses in your criminal defense case, contact us now.