Case File 080 · Investigation and Psychology

How Investigators Test an Alibi

Investigators test an alibi by seeking independent corroboration, but research shows innocent people often struggle to give accurate, well-supported alibis.

By Murder Book Editorial TeamPublished 16 September 2026Updated 16 September 2026

Investigators test an alibi by trying to corroborate it: they look for evidence that does not depend on the suspect's word and check whether it places the person somewhere else at the relevant time. Two broad kinds of support are usually distinguished, physical evidence and the accounts of other people, and the relationship between the suspect and anyone vouching for them matters. Psychology research, starting with a 2004 study by Elizabeth Olson and Gary Wells, shows that people judging alibis tend to find physical evidence more persuasive than support from other people. The same research field has a warning, though. Innocent people often struggle to produce accurate, well-supported alibis, because ordinary memory for where we were on a particular day is poor. A weak or changed alibi is therefore a reason to investigate further, not proof of guilt.

Key takeaways

An alibi is a claim that the suspect was somewhere else when the offence happened; investigators test it by seeking independent corroboration.
In research on alibi believability, physical evidence tends to outweigh support from other people, and people with no reason to help the suspect are seen as more credible.
Law enforcement respondents in one survey said time is critical: the sooner an alibi is checked, the more useful the check is likely to be.
Innocent people frequently give mistaken or weakly supported alibis, and people can misremember where they were on a given day.
Changed or inconsistent alibis are judged harshly, even though honest memory errors can explain them.

What counts as an alibi?

In everyday use, an alibi is a claim that a person could not have committed an offence because they were somewhere else at the time. The law in England and Wales gives a precise version. Section 6A of the Criminal Procedure and Investigations Act 1996 describes evidence in support of an alibi as evidence tending to show that, because the accused was at a particular place or in a particular area at a particular time, they were not, or were unlikely to have been, where the offence is said to have happened.

Rules on alibis differ between countries and legal systems, so this article describes the research and one example framework, not legal advice for any jurisdiction.

How do investigators check an alibi?

At a high level, testing an alibi means asking one question repeatedly: does anything other than the suspect's own account support it?

Corroboration. Investigators look for evidence that confirms or contradicts the claimed location and time.
Independence. Evidence that exists separately from the suspect and their associates carries more weight than evidence that relies on people with a stake in the outcome.
Fit with the wider case. The alibi is compared with the rest of the evidence and placed on the investigative timeline, so gaps and overlaps become visible.
Witness accounts. People named as supporting the alibi may be interviewed, and their accounts compared with the suspect's and with each other. For more on this, see how investigators compare multiple accounts.

In England and Wales, this process has a formal structure. When a defence statement discloses an alibi, section 6A requires it to give details such as the name, address and date of birth of any witness the accused believes can support it, where known. Section 21A of the same Act provides for a code of practice that police must have regard to when arranging and conducting interviews with witnesses notified by the accused. It covers matters such as information given to the interviewee and the accused, and the attendance of solicitors.

Timing matters too. In a 2012 survey of senior law enforcement personnel by Jennifer Dysart and Deryn Strange, respondents consistently said time was critical: the sooner an alibi can be investigated, the more likely the check is to help establish whether the suspect was involved.

What makes an alibi believable to investigators?

The foundational study is Olson and Wells (2004), published in Law and Human Behavior. The authors proposed a taxonomy of alibis based on two kinds of supporting proof: physical evidence and person evidence. Combining different levels of each produced 12 types of alibi. They then asked 252 participants to take the role of detectives and rate the believability of each type.

Believability broadly followed the pattern the taxonomy predicted, with some notable results:

Physical evidence dominated. When physical evidence was present, it tended to outweigh person evidence more than the researchers had expected.
Mistaken strangers were overlooked. Evaluators did not seem to consider that a stranger who corroborated an alibi could simply be wrong about who they saw.
Judgements spilled over onto character. The traits participants attributed to the alibi provider tended to follow how believable the alibi seemed, even when those traits had nothing to do with believability.

The Dysart and Strange survey found that police views matched this pattern. Respondents said the most believable alibis include physical evidence or a statement from an unmotivated person, meaning someone with no reason to support the suspect. But they also reported that suspects provide leads to physical evidence in only about 20% of cases, and estimated that unmotivated strangers lie to police in 12% of cases. Overall, the authors concluded that officers are sceptical of alibi statements.

Study	Who took part	Key finding
Olson and Wells (2004)	252 participants acting as detectives	Physical evidence tended to outweigh person evidence
Olson and Charman (2012)	255 undergraduates	36% of initial alibis turned out to be mistaken
Culhane and Hosch (2012)	Officers, students and laypeople	Changed alibis were viewed less favourably than maintained ones
Dysart and Strange (2012)	Senior law enforcement personnel	Time was seen as critical to alibi investigations
Laliberte and colleagues (2021)	51 adults tracked by smartphone	Participants chose the wrong location 36% of the time

Why do innocent people give weak alibis?

Because most of our days are unremarkable, and memory for unremarkable days is poor. An alibi usually concerns a time the innocent person had no reason to note.

Olson and Charman (2012) asked 255 undergraduates to give alibis for four different times, along with any supporting physical or person evidence. Participants then tried to check that evidence and returned 48 hours later. About 36% of the initial alibis were mistaken, requiring a change to the story or to the supporting evidence. Most of the final alibis relied on evidence that evaluators would consider weak, and alibis for the more distant past were more likely to be mistaken.

A 2021 study by Laliberte, Yim, Stone and Dennis used a smartphone app to record where 51 adults were over a month. A week later, participants were asked where they had been at a given time, choosing from four options. They were wrong 36% of the time. They especially tended to confuse days across different weeks, and similar locations caused more errors than other kinds of similarity.

Taken together, these studies suggest that an honest person can easily be wrong about where they were, and may have little independent evidence to offer even when they are right.

Does a changed alibi mean someone is lying?

Not necessarily, but it is often treated that way. In three experiments, Culhane and Hosch (2012) compared reactions to suspects who changed their alibi statements with reactions to those who kept them the same. Current law enforcement officers, students planning to enter law enforcement and other students all viewed maintained alibis more favourably than changed ones. The authors noted that any lapse in memory for one's timeline could prove damaging to a suspect.

Crozier, Strange and Loftus (2017) argue that this creates a "cascading" risk. Normal memory processes can produce inconsistencies in an innocent person's alibi over time. Those inconsistencies are often misread as deliberate deception, first by investigators, then by prosecutors and finally by juries. A single honest error can end up treated as proof of guilt.

This connects to wider research on why truthful accounts can still be inconsistent and on how confirmation bias can affect an investigation. An alibi that falls apart is information, but it has to be weighed alongside the possibility of ordinary forgetting.

Is there a game about testing stories against the evidence?

Murder Book: The Art of Interrogation is an upcoming narrative-driven interrogation game from Gungrounds, an independent studio in Zagreb, Croatia. It is inspired by real police footage and psychological interviews, and asks players to examine unreliable stories: narrative gaps, avoidance and contradictions. Development screenshots show an evidence board that links statements to one another, such as "I NEVER met her!" and "I had no idea".

The alibi research is a useful reminder when reading a suspect's story. A gap or a changed detail can point to deception, but it can also point to an ordinary person who does not remember an ordinary day. Behaviour and inconsistency are reasons to look closer, not proof, and development screenshots show a case select screen that includes a "not guilty" result.

Murder Book is in development for PC (Steam) and mobile, with release currently planned for the end of Q2 2027. Read What Is Murder Book? for an overview.