Here are the cues that someone could be lying on a call to emergency services

It's not always easy to tell when someone is lying. Research has suggested that good liars use a number of tactics to get away with deception, such as telling plausible stories and being vague about details. These tactics, along with non-verbal strategies, can make it difficult to know when someone is telling the truth.

And it's not just the average person who struggles to work out if someone is being deceptive – even police officers, specifically trained in detecting such behaviour, struggle. This is explored further in a new study, published in Psychological Science, which looks at deception cues during 9-1-1 homicide calls in the United States. It finds a cluster of behaviours that may indicate someone is lying, with potential consequences for the way we deal with emergencies.

The team analysed publicly-available calls placed to 9-1-1 that fit five criteria: they involved the killing of another person, emergency services were notified, the caller communicated the nature of the emergency, at least two news sources could verify who was ultimately prosecuted or admitted guilt, and the caller did not initially confess to wrongdoing. Killings included murders, accidental deaths, and manslaughter.

A total of 41 calls were "deceptive": the callers had either been found guilty of the killing in court or had been deemed to be the killer by medical examiners, police, or grand juries. Deception also required the caller to have either actively lied or lied by omission. A further 41 callers were considered to be "honest".

Three research assistants listened to each call, and reported whether 86 different audio cues were present. For example, they indicated whether the callers were confused, whether they were talkative, and whether they quickly asked for help for the victim.

The results showed that a number of emotionally-related cues were associated with deceptive calls. Deceptive callers were more dramatic, moodier, more reckless, more worried and nervous, more depressed, and more emotional overall.

The team also found that deceptive callers were more likely to tell uncompelling stories that lacked structure, clarity, and purpose – for example speaking in a theatrical way, using non-sequiturs, or self-interrupting. Though we may be liable to believe that pauses in speech and ums and ahs are likely to be seen in those telling lies, there was no evidence of this in this study.

The study has some limitations. Eligible callers were those who had been found guilty; good liars may have remained undetected, successfully hiding both revealing behavioural cues and their culpability. And although the results do provide evidence of certain deceptive cues, it's important to note that you cannot judge someone's innocence or guilt purely on behaviours exhibited during calls to emergency services.

Though the team does suggest that it can be used by law enforcement officers to help identify people of interest, such information cannot be used to make any definitive decisions about who has or has not committed a crime.