The manual defines physical evidence as 'any legally obtained object or material which aids the investigator in the reconstruction of the offense or the identification of the offender.' Uses for physical evidence are as an investigative aid and as proof in court. Instruction on physical evidence at a crime scene focuses on recognition and collection, identification, and preservation. The discussion of recognition and collection encompasses a systematic search, types of material that are of evidentiary value, and comparison samples. Identification issues considered are when to mark evidence, how to mark it, containers, and the information required on the container. Issues in preservation include the prevention of loss, alteration, and contamination. Instruction on physical evidence and the crime laboratory addresses the submission of evidence to the laboratory, the results of analyses and comparisons, and laboratory reports. A discussion of types of evidence focuses on trace evidence, firearms, document analysis, latent fingerprints, and controlled substances. Appended discussions of sexual assault evidence, gunshot residue, delivery of evidence, evidence collection, and the evidence submission sheet.