The Society of Professional Engineers gives their definition of of a forensic engineer:
The best definition of a Forensic Engineer I have found, defines the role as: “Forensic Engineering is the application of the art and science of engineering in the jurisprudence system, requiring the services of legally qualified professional engineers. Forensic Engineering may include the investigation of the physical causes of accidents and other sources of claims and litigation, preparation of engineering reports, testimony at hearings and trials in administrative or judicial proceedings, and the rendition of advisory opinions to assist the resolution of disputes affecting life or property.”
http://www.professionalengineers-uk.org/