How good is an alibi, anyway?

Bad news: the police have brought you in for questioning in a recent murder. The good news, though, is that you didn’t commit the murder! So all you have to do to clear your name is give the police your alibi, right?

Not so fast. Can you remember exactly where you were and what you were doing when the crime was committed? What can you give the police to prove you’re telling the truth? Are your alibi and the evidence supporting it going to be able to convince someone on a jury? Actually, this is going to be more difficult than you thought.

Using an alibi to defend yourself is based on at least two different psychological elements; first, you have to rely on your memory to construct a story of what you were doing. Second, that story has to be believable. That is, you need to supply proof that will convince other people. If you fail at either of these steps, such as by misremembering or not remembering what you were doing or by relying only on a family member to corroborate your story, your alibi probably won’t help you much, if at all.

Try this: Can you remember exactly what you were doing at 1pm a week ago? What about two weeks ago? If you find this a very difficult task, you’re not alone – many of us would struggle to remember what we did several days ago, let alone a longer period. Research on memory backs this up. Unlike a video recorder, our memory is not a running storage of what we’ve experienced. Instead, we only remember some of the information, and even that can decay out of memory very quickly. This means that when we try to remember something, we may only remember a few of the main points and fill in many details with what makes sense, rather than what we specifically remember^1,2,3.

Meanwhile, intuition suggests that if the stakes are high, such as when you’re trying to prove to the police that you’re innocent, our memory can work better⁴. However, if we never fully formed a memory for the alibi event, no amount of focus or effort can make us remember. Further, even if we do form the memory (called “encoding”), we may still fail to recall the memory, or “retrieve” it. You may fail to remember more than few details about what you were doing, or worse, recall the wrong memory. You may remember the wrong day, or you may incorporate incorrect details into the memory – such as someone else’s description of what happened.

Psychology research investigating how people generate alibis demonstrates just how difficult coming up with an alibi can be. In one study, researchers asked participants to remember what they were doing three weeks earlier – essentially, generate an alibi. The participants then spent a few days trying to validate their own alibi and collect evidence to support it, before generating a second alibi. When the researchers compared the first and second alibis, they found the two statements on agreed on about 50% of the details⁵. In a similar study, 36% of the participants changed their alibi after trying to fact-check their first account⁶. These studies demonstrate that even something as simple as trying to remember what you were doing at a previous time and day can be pretty difficult – and that your first attempt will likely contain many inaccuracies.

Many people believe that changes in a story or telling a story out of order is a sign of lying. In fact, under many circumstances, inconsistencies can be more common in true stories than in lies because we make small memory mistakes in recounting what happened. This means that it’s very difficult to remember a specific event without making some mistakes⁷. And if you do make mistakes, the police may think you’re lying to them – obviously not a good position to be in if you’re trying to convince them you didn’t commit a crime.

However, let’s say you have an amazing memory, or get lucky and do accurately remember what happens, your alibi needs to be one that the police can investigate. Can you provide evidence of what you were doing, such as security camera footage or store receipts? This type of evidence would be the most helpful, but may not be available or accessible.

Just because you're concentrating doesn't mean you're remembering better

Can you offer details about what you were doing that are verifiable? For example if you were at home watching TV, could you remember what show you were watching – and what the specific episode was about? Such evidence would allow the police to help verify your alibi, but would be very difficult to remember and may not be enough on its own.

Is there anyone who can confirm what you’re saying? Our friends and family are the people we spend the most time with, and are likely the people we’d go to support our alibi. However, people are inherently skeptical of your friends and family – after all, they may be motivated to lie to protect you. Unmotivated strangers, such as the barista that poured your coffee, or an unmotivated familiar person, such as the security guard you see every day at work, would be best. Indeed, when participants are given proof of an alibi that differs only in who is supporting (and all the other facts of the case are the same), they find alibis supported by an unmotivated stranger or familiar is much more believable than a family member⁸. That of course presents yet another challenge: will they remember you, and will they vouch for you?

Finally, how believable is your alibi? Even if you can collect evidence to support your alibi, you may still run into problems getting the police (or a jury, if you end up on trial) to believe you. For one, both ordinary people and police officers are automatically suspicious of alibis so you’re already fighting an up-hill battle^8,9. Second, not all evidence is created equal. Evidence that is identifying and difficult to fake, such as security footage, would be very convincing¹⁰. However, as mentioned, evidence such as a friend vouching for you is less convincing.

Evidence that would be easy to fake will also be helpful, but not completely convincing. For example, you provide a movie ticket stub for the time in question. At first, this seems helpful – how could you have committed the murder if you were at the movies? But how do we know you didn’t get the ticket from someone else? Or buy the ticket the day before and tear it yourself? Such evidence can certainly help your case – but it’s not going to get you off the hook itself.

A good time, but not necessarily a good alibi.

To summarize, alibis can be very useful forms of evidence to defend yourself against criminal charges – but they aren’t always. First, you have to have sufficient memory to provide an alibi, which involves both encoding information about what you were doing at the time in question, as well as being able to retrieve that information when asked at the police station. This memory test can be easy to fail because you don’t remember enough information, make mistakes, or both. Second, you have to be able to find evidence to support your story. Finally, that evidence needs to be convincing, and not just your best friend saying you were definitely playing video games together.

While the psychology research on underlying memory and social psychology discussed above paints a bit of a bleak picture for alibis, there’s still a lot we don’t understand. For example, we know from research on memory, particularly in educational-oriented areas, that how you ask a question can influence what people are able to remember. In the alibi context, this suggests that how police ask questions can increase memory for an alibi. In fact, one of our current projects is looking at this question exactly*.

A primary challenge to such research is finding strategies that increase the opportunities for innocent suspects to prove their innocence without allowing guilty suspects a chance to construct a lie. One possible strategy for increasing alibi effectiveness would be to allow the suspect to check their own alibi before the police investigate it. For innocent suspects this could be very helpful by allowing them fill in blanks or ask their friends and family for additional information. However at the same time, it would likely benefit guilty suspects as well, allowing them to see if their fake alibi checks out, and changing it if something doesn’t add up.

One promising line of research¹¹ is based on our understanding of how memory retrieval works, which involves promoting the use of more “memory cues.” Have you ever struggled to remember something, and as soon as you think of something related (such as where you were, what you were doing, or someone’s reaction) you suddenly recall it? Or ever noticed how easily you can remember events when you’re in the place where it happened? These are all examples of cues – memories that are tied to other memories, and can help jog our memory.

In the alibi context, this means that if we can get people to use cues, either by helping to generate them through questioning or suggesting a person intentionally try to use them, it may lead to more accurate alibis. This strategy would likely help innocent suspects, who are trying to draw on real memories, while providing little benefit to guilty suspects who are not accessing memories but fabricating a story instead. Of course, this idea still needs to be put to the test in a research lab.

Although psychology research on alibis is relatively new and little, there is a lot of research on the underlying aspects of alibi generation and evaluation. This means that we have a lot of theory on how memory works and how jurors make decisions on which to base future research. We are hopeful that the justice system will consider such current and future research, and adjust policy such that alibis can effectively protect the innocent.

This post was written by Will Crozier / edited by Timothy Luke.

Notes

* To see the details of the project, including our pre-registration, go to osf.io/7nqpc

References

[1] Bartlett, F. C., & Burt, C. (1933). Remembering: A study in experimental and social psychology. British Journal of Educational Psychology, 3(2), 187–192. doi:10.1111/j.2044-8279.1933.tb02913.x

[2] Loftus, E. F. (1996). Memory distortion and false memory creation. Journal of the American Academy of Psychiatry and the Law Online, 24(3), 281–295.

[3] Neisser, U. (1982). Memory Observed: Remembering in Natural Contexts. San Francisco: W. H. Freeman.

[4] Kassam, K. S., Gilbert, D. T., Swencionis, J. K., & Wilson, T. D. (2009). Misconceptions of memory the Scooter Libby effect. Psychological Science, 20(5), 551–552. doi:10.1111/j.1467-9280.2009.02334.x.

[5] Strange, D., Dysart, J., & Loftus, E. F. (2014). “Oops, I guess I made a mistake”: Why alibi errors are not necessarily evidence of guilt. Zeitschrift für Psychologie, 222, 82–90. doi:10.1027/2151-2604/a000169.

[6] Olson, E. A., & Charman, S. D. (2012). ‘But can you prove it?’ – examining the quality of innocent suspects’ alibis. Psychology, Crime, & Law, 18(5), 453–471. doi:10.1080/1068316X.2010.505567.

[7] DePaulo, B. M., Lindsay, J. J., Malone, B. E., Muhlenbruck, L., Charlton, K., & Cooper, H. (2003). Cues to Deception. Psychological Bulletin, 129, 74-118.

[8] Culhane, S. E., Hosch, H. M., & Kehn, A. (2008a). Alibi generation: Data from US Hispanics and US non-Hispanic whites. Journal of Ethnicity in Criminal Justice, 6(3), 177–199. doi:10.1080/15377930802243395.

[9] Dysart, J., & Strange, D. S. (2012). Beliefs about alibis and alibi investigations: A survey of law enforcement. Psychology, Crime, & Law, 18(1), 11–25. doi:10.1080/1068316X.2011.562867.

[10] Olson, E. A., & Wells, G. L. (2004). What makes a good alibi? A proposed taxonomy. Law and Human Behavior, 28(2), 157–176. doi:10.1023/B:LAHU.0000022320.47112.d3.

[11] Leins, D. A., & Charman, S. D. (2016). Schema reliance and innocent alibi generation. Legal and Criminological Psychology, 21, 111–126. doi:10.1111/lcrp.12035.