It is a common trial strategy for an attorney to attack inconsistencies within testimony offered by a victim, witness, or an investigator. And yet most victims, witnesses and investigators tell the truth when testifying. On the other hand, consider a suspect who told an arresting officer that a friend drove him home on the night of a crime. Several hours later the suspect tells an investigator that he drove himself home that night. This inconsistency supports the opinion that the suspect has principal or secondary involvement in the crime under investigation. However, not every inconsistency in a suspect's statement supports deception. In fact, when an account is repeated two or three times with perfect consistency this should be viewed suspiciously. The question then becomes, when do inconsistencies in an account support deception?

It is first important to distinguish between inconsistencies and omissions between two statements. An inconsistency refers to a change of fact between two accounts. When a subject initially reports that on a particular afternoon he was golfing with friends and later recalls that on the afternoon in question he was watching a football game alone in his apartment, this is an inconsistency. An omission, on the other hand, refers to information left out of an original account that is included in a subsequent statement. During our training seminars we show the interview of a woman who fabricated a story that she was abducted from a parking lot. While her statements were all consistent, during her initial description of the assault she omitted the very significant detail that the abductor had a knife.

A second important consideration is whether or not a suspect's statement represents a true inconsistency. A security guard suspected of arson may state at one point during an interview, "I checked the floors around 8:00 and didn't smell any smoke -- everything was fine. I don't believe I entered any of the rooms. I just walked the halls." Later, he may acknowledge that it is possible that he checked the floors as late at 8:15 and may have entered some rooms, because he occasionally does this. The guard did not contradict himself because he used qualifying phrases in his first statement ("around" and "I' don't believe").

A naive investigator may believe that if a person is telling the truth there should be a perfect correlation between two accounts relayed at different times. However, there are circumstances when a truthful person may provide inconsistent objective recollections of what happened, when it happened and even where it happened. The two most important factors to consider when evaluating inconsistencies are the passage of time between the event and its recollection as well as the significance of the event. Consider a suspect who initially reported that two weeks ago Friday when he arrived home from work his wife was out shopping. After talking to his wife or giving more thought to the evening, he may now recall that she had already returned from her shopping trip by the time he arrived home. This inconsistency should, in no way, tarnish his overall credibility.

Conversely, consider the suspect who initially reported that his wife struck him with a frying pan which caused him to grab a knife to fend off her attack at which time he stabbed her. During a subsequent interview he now acknowledges that, because he was cooking, he already had the knife in his hand at the time his wife struck him with the frying pan. The cause-effect relationship between being struck and grabbing a knife is certainly significant and it is highly improbable that a person could somehow be confused as to the sequence of these two events.

A person's state of mind at the time of an event should also be evaluated. Intense emotions (anxiety, fear, pain) or intoxication may certainly influence an individual's recall. However, such conditions should be associated more with omission and memory qualifiers (I believe, etc.). When a person who was admittedly intoxicated or frightened at the time of an event expresses no uncertainty in recollections and offers an inflexible version of events the investigator should be suspicious of the veracity of the recollections.

Finally, possible motivations for inconsistent statements must be assessed. A rape victim may initially report that the assailant pulled down her jeans and later change her statement indicating that she undressed herself at the man's instruction. This inconsistency makes perfect sense since many legitimate rape victims are initially reluctant to acknowledge any level of cooperation with the rapists, including engaging in friendly conversation with him before the attack. In instances where a suspect is interrogated and subsequently identified as being innocent, it is often because the suspect previously lied about his alibi, access, motive or involvement in a crime unrelated to the issue under investigation.. In each of these cases, the suspect will be able to articulate a reasonable explanation for the earlier lie. A suspect may explain that he offered a false alibi to avoid disclosing that he has been having an affair. He may acknowledge lying about knowing the victim for fear of becoming a suspect in the investigation or lie about being behind on bills (having a financial motive) for the same reason. We are not suggesting that when these types of inconsistencies surface during an investigation that they indicate truthfulness. In fact, they often support deception. What is being suggested is that when these circumstances exist the innocent suspect is able to offer a plausible explanation for his previous lie.

The following guidelines are offered to interpret suspect inconsistencies that support the opinion of deception:

1.	The inconsistent event is significant in nature and would not likely to be forgotten.
2.	There are inconsistencies in the sequence of significant events that relate to cause-effect relationships during a crime.
3.	The subject changes his statement after being challenged either with actual or fictitious evidence e.g., "If we were to talk to neighbors in that area would any of them tell us they saw your car in her driveway that day?" "Now I remember. I actually did go to her house that day and drove in the driveway but decided not to go in."
4.	The suspect rigid in recollections of remains facts that are usually estimated, e.g., " Three weeks ago I was at Tom's house from 7:10 until 10: 40."
5.	Even though the suspect was under the influence of alcohol or drugs, he exhibits no uncertainty as to his recollections of minor events, e.g., "I am certain that just before this happened Julie stopped playing pool and went into the bathroom knowing that John was in there. She was in the bathroom for seven minutes and when she came out she had a smile on her face and her blouse was untucked.."
6.	The suspect is unable to offer any reasonable explanation for his earlier inconsistency.

The following inconsistencies would not necessarily support deception and may, in fact, indicate the normal memory process of a truthful person:

1.	Small discrepancies in estimates of time or distances
2.	The event represents an everyday behavior for the subject
3.	A significant time period elapsed between experiencing an insignificant event and relating it
4.	The suspect has a rationale explanation for his inconsistency, e.g., "After reviewing my calender I remembered that ..."
5.	A suspect who lies about his alibi to cover an embarrassing event (being with a prostitute), protect a friend or prevent disclosure of an illegal activity unrelated to the crime (using drugs at a friend's house).
6.	A suspect who lies about access or motives and, when interrogated, sincerely states that he did not reveal this information earlier because he was afraid it would make him look guilty.

In conclusion, significant inconsistencies in a suspect's statements certainly supports an opinion of deception to the issue under investigation. These are most likely to occur when the investigator challenges the suspect's original statement with real or fictitious evidence. Most guilty suspects are able to relate a consistent account because they keep their stories simple. Innocent suspects, who are anxious to get everything right, may offer minor inconsistencies between two accounts.