Contaminating a Subject's Behavior

Written By: Reid
Jul 01, 2003

When inferring deception from a suspect's behavior, investigators must remember that a subject's outward behaviors during questioning are not direct signs of lying. Rather, when a person lies behavior symptoms such as poor eye contact, stammering or foot bouncing are the product of underlying emotions associated with the fear of having the lie detected. These observation are called "symptoms" because none of them directly indicate deception. To determine if an observed behavior is a possible symptom of deception, the investigator must eliminate other variables which may cause the same behavior. In other words, even though the behavior was present, if it was contaminated because of some external or internal factor the investigator should not consider the observation as a reliable indicator of deception.

Consider a high school student who is pulled over for speeding. It is an April evening in Wisconsin and the outside temperature is about 40 degrees. The driver is an honor student who just completed a day of performing music events for state competition and is late getting to a friend's birthday party. In his haste to get to the party he did not put on a jacket. Furthermore, he wears his hair long and has a quiet, thoughtful personality. The officer asks him to step out of the vehicle to gather general information and observes that the driver visibly shaking and responding softly to questions. Based on these observations, a field sobriety test is conducted wherein the officer asks the young man to repeat the alphabet backwards as fast as he can. The driver, of course, is unable to do this and the officer engages in a field interrogation to elicit an admission of alcohol or drug use. After no admission was forthcoming and a search of the vehicle yielded no evidence, the young man was issued a citation and allowed to go to the birthday party.

This officer arrived at an erroneous opinion of suspecting drug or alcohol use because he failed to take into consideration variables that influence a person's behavior. Being underdressed and exposed to a 40 degree temperature will cause even the most honest person to shiver. Some people, by nature, are soft spoken whether talking about their family or job or answering questions regarding possible involvement in a crime. An investigator who relies upon behavioral observations to establish reasonable suspicion or probable cause must be aware of factors that contaminate behavior symptoms.

Establishing Normative Behaviors

At the outset of any interview an investigator should ask non-threatening background questions to establish baseline behaviors and make other important assessments. The three most important areas in which to establish normal behaviors are eye contact, speech characteristics and general nervous tension. There are many natural causes for poor eye contact including low self esteem, cultural upbringing and emotional states such as embarrassment or shame. There is a wide range of normal speech patterns within the population. Under normal circumstances some people speak quite loudly while others speak softly. Some individuals speak very rapidly while others draw out their words or have periods of silence in the middle of a sentence as they collect their thoughts. Similarly, a subject's general nervous tension can vary widely. Some people, with the slightest source of anxiety, will display signs of anxiety release such as pacing, laughing, foot bouncing, gum chewing or hand wringing while others maintain their composure and display no manifestation of anxiety even in a crisis situation. Once a subject's normal behavior is established the investigator can then look for changes in that behavior when questions concerning the issue under investigation are asked. The other important initial assessments to make while asking non-threatening questions are the subject's intelligence, language skills, mental health and physical impairments (medical conditions, fatigue, stuttering, etc.) as each of these internal factors may lead to a misdiagnosis of the subject's behavior.


When conducting an interview the investigator should sit about 4 - 4 Ohm feet in front of the subject. If both people are standing the distance can be shortened to about 2 Ohm - 3 feet. If the investigator sits or stands too close to a subject the subject will feel threatened and may engage in protective behaviors. These include moving away from the investigator, turning the lower body away from the investigator, crossing arms and legs, and offering abbreviated responses. These, of course, are classic deceptive behaviors but can be induced from a truthful person as a result of proxemics.


It is normal for the average citizen to experience some anxiety when talking to a law enforcement officer even though the officer is acting professionally and is, in no way, intimidating. However, when the officer's attitude is perceived as threatening, this may cause apparent deceptive behavior from a truthful person. When the young man referred to earlier initially denied using any drug or alcohol the police officer responded by saying, "I don't like to be lied to!" This remark set the tone for the entire field interrogation. An investigator who comes across as judgmental, condescending and intimidating will invoke defensive behavior from a subject. Under this circumstance some subjects will respond by refusing to answer questions, making accusations of racial or ethnic biases, threatening a law suit, increasing the volume of their voice and aggressiveness of their body language. Other subjects will respond to this threat by withdrawing. These subjects may exhibit poor eye contact, respond to questions softly, become confused to the extent of offering inconsistent information or assume a guarded attitude where they volunteer little information.


An ideal environment in which to observe behavior symptoms of deception is controlled. It will have a comfortable temperature and there will be no visual or auditory distractions. Of key importance, the environment will be private i.e., the investigator and subject will be alone in the room. Realistically, however, interviews are conducted in many different environments, and these variations must be taken into consideration. A subject who is interviewed in a holding cell where the temperature is 95 degrees may sweat profusely even though he is telling the truth. A subject who is questioned facing the sun or under bright lights will exhibit poor eye contact. Similarly, a suspect who is questioned by someone wearing dark sunglasses will tend not to look at the other person's eyes. A subject being questioned in the presence of family members or co-workers may exhibit poor eye contact, guarded or evasive responses and a closed posture not because of deception, but because of the awareness that others can see him being questioned.

Question Formulation

Even when an interview is conducted in a controlled environment and the investigator's attitude is non-judgmental and sitting a proper distance from the subject, behavioral contaminations can still result because of the manner in which questions are asked during the interview. John E. Reid and Associates is often consulted to review video-taped interviews and interrogations to offer guidance to an investigation. The following are the most common contaminations that cause difficulty in this task:

1. Failure to distinguish between an interview and interrogation. An interview should be non-accusatory whereas an interrogation is accusatory and involves active persuasion; they are two separate and distinct procedures. There are a number of behavior symptoms which have opposite interpretations depending on whether they occur during an interview or interrogation. If an interaction between a subject and investigator starts out non-accusatory but the investigator then challenges the subject's statement or accuses the subject of lying, this changes the dynamics of the interaction. Even if the investigator returns to a non-accusatory tone, the subject's behavior has been contaminated. An often repeated message in our seminars is, "If you are going to interview, interview. If you are going to interrogate, interrogate o don't mix the two."

2. Failure to make behavior-provoking questions issue specific. Consider that two truthful suspects are interviewed on a sexual assault. The first is asked, "Have you ever thought about forcing a woman to have sex with you?" The second is asked, "Have you ever thought about doing something like this?" The first suspect responds, "Absolutely not." The second responds, "Well, this is a strange situation for me to be in and I never in my wildest dreams thought I'd ever be accused of doing something like this." Both suspects are telling the truth, yet because of the ambiguous manner of asking the second question, the suspect's response appears evasive.

3. Tagging questions. When a suspect is asked, "Did you see (victim) on the day of her death?" an early or late denial can be a strong indication of deception. However, if the investigator continues to talk after asking a question a truthful subject may answer the question too early providing a misleading symptom of deception. The following is an example of a tagged question: "Did you see (victim) on the day of her death. I'm not suggesting you killed her or anything but did you just see her that day?" In addition, tagging a question buys time for a deceptive suspect to formulate a comfortable response which may result in what appears to be an on-time response. The lesson here is to keep questions short and succinct o place anxiety on the potentially deceptive suspect, don't remove it.

4. Suggesting answers. The purpose for asking behavior-provoking questions is to draw out the suspect's underlying attitudes toward the investigation. An investigator can significantly affect a suspect's response to these questions by suggesting possible answers. As an example, consider the following improperly asked question: "Do you think the person who left the scene of that accident should be sent to jail?" A deceptive suspect may well agree with the investigator's suggestion. The proper way to ask this question is, "What do you think should happen to the person who left the scene of that accident."

5. Asking questions too quickly. During our seminars we emphasize the importance of note-taking during a formal interview. The primary importance of note-taking is that is slows down the pace of questioning. It is much easier to lie to a series of questions that are asked rapidly than questions that are separated by a period of 5-7 seconds of silence as the investigator writes out the suspect's response. A deceptive suspect is uncomfortable with silence created during note-taking and often exhibits many significant behavior symptoms while the investigator is writing out his response. Conversely, a rapid-fire questioning approach may cause an innocent subject to become confused and offer inconsistent information.


Field studies investigating the accuracy of behavior symptom analysis report impressive findings. It is important to remember that the interviews analyzed in these studies were conducted in a manner that eliminated or minimized possible contamination of the subject's behavior symptoms. On the other hand, many of the laboratory studies which have produced low accuracy rates for detecting deception have failed to control for variables which influence a subject's behavior symptoms. Contamination of a subject's behavior is a real effect and should not be ignored by researchers or individuals who work in professions that rely on making inferences from a person's behavior.

Law enforcement officers rely extensively on their ability to "read" a person based on behavioral observations. In making these assessments it must be remembered that there are both innocent and guilty possible causes for the same behavior. A behavioral observation only becomes a reliable symptom of deception when the investigator can eliminate other possible causes for the behavior.

To learn more about factors that affect a subject's behavior consider attending out three-day basic course on interviewing and interrogation techniques.

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