Expert Witness Testimony

Expert witness testimony can significantly impact the outcome of a trial. Both California Evidence Code sections 720-721 and Federal Rules of Evidence Rules 702-703 provide guidelines for the admissibility and limitations of expert witness testimony.

In California, expert witnesses are governed by Evidence Code Sections 720-721, which outline the criteria for qualification. A witness may be considered an expert if they possess “special knowledge, skill, experience, training, or education” that allows them to provide testimony that is beyond the common knowledge of the average person.

For example, in a murder trial, the defense seeks to introduce a forensic pathologist as an expert witness. The pathologist has extensive education, training, and experience in forensic medicine, making them qualified to testify about the cause of death and other relevant forensic evidence. Due to their specialized knowledge, the court may qualify the pathologist as an expert witness.

In California, pursuant to Evidence Code section 352, the court has the authority to limit or exclude expert testimony if it determines that the testimony is unreliable, irrelevant, or will unduly consume time.

For example, in a DUI trial, the prosecution calls a forensic scientist as an expert witness to testify about DNA evidence. The defense attorney argues that the expert’s methodology and analysis were flawed and unreliable. The court may choose to limit or exclude the expert’s testimony if it finds that the testimony lacks reliability.

Under the Federal Rules of Evidence, Rules 702-703 govern the qualification of expert witnesses. Rule 702 states that a witness may be qualified as an expert if they possess “scientific, technical, or other specialized knowledge” that will help the trier of fact understand the evidence or determine a fact in issue. Additionally, Rule 703 allows experts to base their opinions on facts or data that are reasonably relied upon by experts in their field.

For example, in a federal firearm trafficking case, the defense wishes to present a ballistics expert who has years of experience in the study of firearm trajectories and can testify about the bullets’ origin. The court may qualify the expert witness based on their specialized knowledge.

Under the Federal Rules of Evidence, Rule 702 empowers the court to exclude expert testimony if it determines that the testimony is not helpful to the trier of fact, lacks reliability, or is based on unreliable methods or principles. Rule 703 further permits the court to limit the basis for an expert's opinion or to require disclosure of the underlying facts or data.

For example, in a federal drug trafficking trial, the prosecution offers the testimony of a chemist as an expert witness to identify the seized substances. The defense attorney argues that the chemist used outdated and unreliable testing methods. The court may exclude or limit the expert's testimony if it finds the methodology unreliable.

Defense attorneys can encounter several challenges when dealing with expert witnesses.

Qualification Challenges: Defense attorneys must evaluate the qualifications of prosecution expert witnesses and, if necessary, challenge their qualifications if they believe the witness does not meet the criteria for expertise.

Reliability Challenges: Defense attorneys may challenge the reliability of an expert's testimony, pointing to inconsistencies, flawed methodologies, or a lack of scientific consensus.

Limitation Strategies: Defense attorneys may seek to limit the scope of an expert's testimony or request the court to exclude certain portions that are deemed irrelevant or prejudicial.

If you have been charged a crime, it is critical that you discuss your case immediately with a knowledgeable and aggressive criminal defense attorney as soon as possible.  As a former Deputy District Attorney with over 14 years of prosecutorial experience, Los Angeles criminal defense attorney Michael Kraut has an in-depth knowledge of expert witness testimony in both California and federal cases.

For more information about the criminal justice process, and to schedule your free consultation, contact Michael Kraut at the Kraut Law Group located at 6255 Sunset Boulevard, Suite 1520, Los Angeles, CA 90028.  Mr. Kraut can be reached 24/7 at (323) 464-6453.