The primary investigation uses a macro approach compared to the micro approach used in determining the point of origin of the fire. Factors to consider in the primary investigation include the structure location, weather, time of incident, security, discoverer of the fire, etc. The basic characteristics of the structure should be noted in documentation. A perimeter search should also be documented. Steps in determining the point of origin of the fire include (1) going back some distance from the fire scene to see if any 'V' pattern exists, which is customarily a reliable indicator of point of origin; (2) checking for deep charring if no apparent 'V' pattern exists; and (3) noting light bulbs, wax candles, and certain plastics deformed and drawn toward the point of origin. Arson is indicated by multiple points of ignition; large alligatoring char with sheen, which indicates a fast and very hot fire, such as from a flammable liquid; and traces in samples of floor material of hydrocarbons used in setting the fire. Evidence should be classified as direct, primary, secondary, prima facie, circumstantial, hearsay, and opinion. Care should be taken to preserve and document the location of evidence. The taking of photographs and the noting of fire ground information should begin immediately. Investigators should develop the basic skills of interviewing witnesses. Should investigators be involved in the interrogation of suspects, questions should be carefully outlined and previewed with the prosecutor to eliminate any legal problems. Interrogation should begin only after all information and evidence has been collated. Four footnotes and one bibliographic listing are provided.