The Alibi: Eyewitness to Innocence

“Suppose you discovered, much to your surprise, that you were considered a sus- pect in a criminal investigation. You are innocent, so you simply have to account for your whereabouts for the time of the crime. If you remember where you were at the time of the crime, you have an alibi—an alibi is simply a claim that you were elsewhere. However, having an alibi is the easy part; proving an alibi is another matter altogether”.

Just as police and prosecutors seek out eyewitnesses to identify suspects and build a case against them, defendants often call on their own witnesses, or alibis, to help vouch for their whereabouts at the time of the crime. There are several ways that someone under suspicion can offer proof of innocence. Sometimes physical evidence can be used—such as ATM receipts, cell phone or GPS records, or surveillance video. At other times, other people are cited—such as a spouse, friend, neighbor, cashier, or waitress.

How honest are alibi witnesses? Are they willing to lie for someone they know and like? Are their memories subject to influence from outside sources? To answer these questions, Stephanie Marion and Tara Burke (2013) devised an ingenious experiment in which they brought student participants into the lab with student confederates hired to act as co-participants on several tasks. At the start of each session, determined by random assignment, some student pairs were led to believe that personality tests they had earlier taken showed them to be very similar, at which point they worked together on the first task and had a friendly conversation. Other student pairs were led to believe that they were dissimilar, at which point they were separated to work on the first task in different rooms. Sev- eral minutes into every session, the confederate left to use the restroom. She then returned to the lab with cash in her pocket, which she then placed in her wallet, or without any sign of money.