When recording the data at a scene, the security officer must employ his or her senses, primarily sight and secondarily hearing, smell, and touch. Security officers should never intentionally use their sense of taste in an effort to test a substance. The many examples displayed on television where the private investigator or police detective touches a substance and announces the contents (e.g., “This is pure heroin!”) are simply farces. To taste a substance that could be lethal may result in the death of a security or law enforcement officer. The eye is the greatest source of information; however, in the absence of training, it is also one of the most unreliable because of the tendency of the observer to fill in the gaps that inadequate observation may leave. Hearing is the most objective sense; however, the observation of sound is subject to errors, such as mistaken estimates of distance and illogical comparisons. The sense of touch is usually unreliable because of the inexperience of most persons in the accurate use of this sense. Smell is considered to be for the most part unreliable because it is easily swayed by suggestion. The sense of taste suffers from the same defect.

If a person is a witness to an incident involving violence to another person with whom they are emotionally close—such as a mother, father, daughter, son, husband, or wife—their observations may have been altered. Consider a mother who witnesses the death of her child from injuries sustained in an automobile accident. The mother may not be able to recall specific details about the incident or she may be able to provide explicit details because the event is so ingrained in her mind. The emotional attachment has affected her observation and memory.

For the security officer, the process of observation can be divided into three stages: attention, perception, and report.

The ability to describe a person accurately is invaluable to a security officer. Often, this ability is not present in most people, including security officers. For the most part, security officers have received little training in the proper way to describe individuals.

The search of the incident or crime scene is in many cases the most important part of any investigation. Nonviolent offenses, such as employee theft, will normally not involve a crime or incident scene. Crimes of violence, however, do involve physical contact with the victim and the immediate surroundings. Traces of the criminal may be left in the form of clothing, shoe impressions, fingerprints, blood stains, damaged furniture, etc. A trained investigator will be able to visualize the way in which the criminal carried out the offense. Samples of clothing, carpet, hair, human bodily fluids, fingerprints, etc., may all remain as part of the crime scene.