There are a number of behavioral characteristics which tend to support or refute the validity of an alibi. To take advantage of these, the investigator must elicit an alibi in a manner which provides the most meaningful of information. Consider a home invasion where a jeweler was robbed by a man last Friday night at 7:30. The traditional interview question asked to elicit this suspect's alibi would be, "Where were you last Friday night at 7:30?" The suspect may respond, "I was shopping at K-Mart for a birthday present for my nephew." Follow-up questions may reveal that the suspect purchased a football, for which he paid $25.00 cash, but he did not keep his receipt. Furthermore, the suspect denies encountering anyone he knew during his shopping trip. Is this alibi true or false? Given this limited information it is impossible to tell. Suppose, however, that the suspect was asked the following question to elicit his alibi: "Tell me everything you did last Friday night from 6:00 until 9:00." This question offers the potential for much more meaningful information. Because it does not reveal the time of the crime (7:30), the innocent suspect's detail and recollections of his activities should be similar before and after the commission of the crime. The deceptive suspect, however, knows when he committed the crime and this guilty knowledge may influence his recounting of events. He may offer sketchy information prior to and after the commission of the crime, but very specific details at the time of the crime (a rehearsed alibi). On the other hand, the guilty suspect may tell the truth about his general activities before and after the crime, which includes a fair amount of detail, but he conveniently glosses over the details of his whereabouts at the time the crime was committed (an unprepared alibi). Some crimes involve incriminating activities before and after the actual commission of the crime. Under this circumstance, the guilty suspect must fabricate most of his account, where the entire account tends to be vague. Consider the following two responses to the question, "Tell me everything you did last Friday night between 6:00 and 9:00."
SUBJECT 1: "At 6:00 I had just arrived home from work and I took a shower because I knew I was going to go out for pizza. I had already arranged with a friend from work, Rick Johnson, to meet at the Pizza Hut on Sunset Ave. We were going to meet there at 8:00. Rick was bringing a date and I wanted to bring one too but I didn't get a chance during the day to call anyone. Around 6:30 I called Betsy King, a girl I dated in high school and occasionally go out with, but there was no answer so I ended up going alone. On Saturday my brother was having a birthday party for my nephew Paul and I hadn't yet gotten him a present. There is a K-Mart right across the street from the Pizza Hut so I left my apartment at around 7:00 and got to the K-Mart at maybe 7:15. I knew I was going to get him a football so I picked one out and then, to kill time, I looked at camping stoves and lanterns. Next month I'm going to go with some friends on a camping trip up North and I still need some basic equipment. At any rate, I only bought the football and that would have been around 7:45 or so. I went right from the K-Mart down the street to the Pizza Hut and arrived before Rick and Gloria. I ordered a beer while I waited for them and they arrived a little after 8:00. We ordered a pizza and a pitcher of beer and we were there until after 9:00. We left together and I didn't get home until about 9:30."
SUBJECT 2: "At 6:00 I was just hanging in my apartment and I needed to buy a present for my nephew's birthday so I went to the K-Mart on Sunset and bought him a football. At 7:30 I was inside K-Mart buying the football. I paid $25.00 cash for it in the express lane. Eventually, I left and went out for pizza at Pizza Hut. I think I was still at the Pizza Hut at 9:00 because I didn't get home that night until later."
In analyzing these two alibis, the first appears to be much more credible than the second. In addition to the details offered within the first statement, other indications of truthfulness include: 1. Specific information with respect to time, people's names and locations; 2. The account contains unnecessary information (thoughts, things that were not done); 3. The account follows the suspect's normal behavior, e.g., he has gone out with these friends for dinner in the past and often dines in at this Pizza Hut. On the other hand, the second alibi is sketchy except for the time period of the crime. It contains the following deceptive criteria:
1. Vague information with respect to time, people's names and locations;
2. The absence of unnecessary information the account focuses on behaviors to connect one event to the other;
3. "Time-gap" phrases that indicate something is being left out of the account, e.g., "after a while", "eventually", "the next thing I knew";
4. The account may not represent the suspect's normal behavior, e.g., this is only the second time in 10 years that the suspect has eaten at this particular Pizza Hut he almost always orders a pizza for delivery. A key in eliciting a meaningful alibi in this manner is to instruct the suspect to tell you everything that he did between two time periods (generally a couple of hours before and after the crime). A question such as, "Tell me what you did last Friday night," will often result in a general accounting of events from both the truthful and deceptive suspects.
For further information to help identify the validity of an alibi, see The Investigator Anthology, pp. 23 - 28.