Single fingerprint at a crime scene 'detects cocaine usage'

A single fingerprint left at a crime scene could be used to determine whether someone has touched or ingested cocaine, scientists say

  • Cocaine’s primary metabolite – benzoylecgonine – is excreted in fingerprints
  • But this is only the case when the drug has been ingested, rather than touched 
  • Experts say they can use mass spectrometry to make this important distinction

A single fingerprint could be used to determine whether someone has touched or ingested class A drugs, a new study reveals.

Researchers at the University of Surrey say mass spectrometry can be used to detect benzoylecgonine in a print that’s been left behind at a crime scene. 

Benzoylecgonine is a molecule produced in the body and excreted in fingerprints when cocaine is ingested but not touched.  

It is therefore essential in distinguishing those who have consumed the Class A drug from those who have handled it. 

Police need experts to distinguish between people who have handled cocaine from those who have ingested it, because the legal ramifications are different – for example, drug driving. 

Cocaine is taken by 70 per cent of all UK drug users, according to drug charity We Are With You, and investigating the role it may have played in a criminal setting is vital. 

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A single fingerprint at a crime scene detects class A drug usage, thanks to benzoylecgonine, a molecule produced in the body when cocaine is ingested, researchers at the University of Surrey reveal


Mass spectrometry (MS) is an analytical detection technique used to determine information about individual chemical molecules.

MS is based on ionisation and fragmentation of molecules in the gas phase.

Since molecules fragment in a unique manner, the resulting ion fragmentation pattern can be used to obtain structural information for a given molecule.

In forensic science, MS has become the technique of choice for the definitive identification of a wide variety of evidence. 

The study has been conducted by researchers at the University of Surrey in collaboration with the National Physical Laboratory (NPL) in southwest London and Southampton-based technology manufacturer Ionoptika Ltd. 

The experts used three mass spectrometry imaging approaches – which measures the characteristics of individual chemical molecules – to analyse fingerprints.  

‘In forensic science being able to understand more about the circumstances under which a fingerprint was deposited at a crime scene is important,’ said Dr Melanie Bailey at the University of Surrey. 

‘The new research demonstrates that this is possible for the first time using high resolution mass spectrometry techniques.

‘These new findings will inform forensics further when it comes to determining the use of class A drugs.’

The new study, which been published in the journal Analyst, is an advance on research published by the team in February last year. 

At the time, researchers revealed they were able to determine the difference between touching and ingesting cocaine on fingerprints – but only if someone had washed their hands prior to giving a fingerprint sample. 

‘If hands are not washed, we can see benzoylecgonine in both drug users and people who have touched the drug,’ said Dr Bailey.

‘This is because benzoylecgonine is an impurity in street cocaine.

‘When hands are washed, the benzoylecgonine from contact washes off. In contrast, someone who has consumed the drug continues to excrete benzoylecgonine from their fingertips.’ 

If someone has taken cocaine, benzoylecgonine correlates with other compounds produced in the body, all excreted along the fingerprint ridges.

In contrast, if someone has touched the drug, cocaine and benzoylecgonine ‘hotspots’ do not match the location of the fingerprint ridges.

If a suspect is in custody, authorities can simply tell them to wash their hands and give a fingerprint sample, to find if they took or handled the drug.  

But it’s a different story when fingerprints are left at a crime scene, and authorities don’t necessarily know anything about the circumstances under which the prints were deposited. 

And when someone unwillingly leaves fingerprints at a crime scene – whether they’re a victim or a criminal – they’re unlikely to have washed their hands just prior to doing so. 

This had meant the distinction between whether cocaine had been ingested or handled by people who left fingerprints at the scene couldn’t be made.  

‘The new research gets us further along the road to reconstructing the events that took place at a crime scene,’ Dr Bailey explained to MailOnline. 

‘Now we think it is possible to tell, from a fingerprint left behind at a crime scene, whether or not someone has touched or ingested cocaine. We couldn’t do this before.’ 

A criminal who is forensically aware may wash their hands, but they may also wear gloves to avoid leaving fingermarks in the first place, Dr Bailey pointed out. 

‘Despite this, fingermarks are still the most commonly used piece of physical evidence left at a crime scene in forensic case work,’ she said.              

Alcohol triples a person’s likelihood of taking cocaine 

Alcohol is a gateway drug and can influence someone’s likelihood of becoming addicted to cocaine, a 2017 study claims.

Columbia University Medical Center researchers analysed the behaviour of ‘gateway drugs’ and how they can impact the body’s response to other substances.

They evaluated rats who were given alcohol ten days prior to having cocaine, and those that were exposed were more vulnerable to showing addictive behaviour.

The rats that had alcohol were three times more likely to be addicted to cocaine, the team found.

Rats that were exposed to alcohol before using cocaine pressed a lever 58 times to signal they wanted more of the drug.

Alternatively, rats that were not exposed to alcohol before using the drug only pressed the lever 18 times to signal they wanted more of the drug.  

The study authors warned that this gateway drug can influence the brain in how it responds to other substances.

Read more: Alcohol triples a person’s likelihood of taking cocaine

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