A forensic engineering expert witness investigates materials, products, structures or components that fail or do not function as intended which may cause personal injury or damage to property. The consequences of failure are dealt with by the law of product liability. The subject is applied most commonly in civil law cases, although may be of use in criminal law cases. Generally the purpose of a forensic engineering investigation is to locate cause or causes of failure with a view to improve performance or life of a component, or to assist a court in determining the facts of an accident.
Methods used in forensic investigations include reverse engineering, inspection of witness statements, a working knowledge of current standards, as well as examination of the failed component itself.
Excerpted from wikipedia.com.