Industry News

Latest News

The Role of Forensic Science in the Criminal Justice System

04 May 2012

By Simon Franc


Forensic scientists have a very important role in the criminal process: from initial crime scene investigation to forensic laboratory analysis to providing expert forensic statements and culminating in their appearance in court as an expert witness. Forensic scientists do not just perform forensic analyses and report on the results. As expert witnesses they are allowed to provide opinion as well factual evidence in criminal cases.  Interpretation of certain factual evidence and opinions relating to it may vary between forensic experts; which is where forensic defence experts come in to the equation. Many will be extremely experienced and long serving forensic scientists who can use their experience and expertise to re-examine the forensic evidence and peer review any statements from the Crown’s experts. Where appropriate, they can offer alternative forensic expert interpretation and opinion and appear in court as an expert witness for the defence.


Forensic science is divided into several disciplines and most forensic scientists who act as expert witnesses will usually specialise in one or two particular disciplines, which is what makes them ‘experts’  rather than just someone with a general knowledge of forensic science as a whole.  These forensic disciplines include Forensic Biology and DNA, Forensic chemistry (which includes marks and traces), Forensic Drugs, Forensic Toxicology, Fingerprints, Firearms and ballistics and Road traffic accident investigation.  In many serious criminal cases the trial may involve obtaining forensic evidence from forensic scientists in a whole range of forensic disciplines.


To get a better idea of the role of the forensic scientist let us consider a few case scenarios:


1. The crime scene of a violent assault/murder where the victim’s body is still at the scene.


At a crime scene of this nature there may be contact trace exchange, such as blood, DNA, hairs, fibres etc. between the victim and their assailant. This will involve a forensic biologist and necessitate forensic DNA analysis as well as fibre analysis, blood pattern analysis and should also include the examination of the victim’s and suspect’s clothing.  All of this forensic evidence can then be interpreted by an expert forensic biologist. 


There may be blood stains, smears and splashes, all of which if interpreted correctly by an experienced expert forensic biologist can indicate a possible scenario of what took place at the crime scene before and after the victims death. 


There may be fingerprints to be lifted and examined by a fingerprint expert and shoeprints to be photographed and compared by a forensic chemistry expert to shoes found on the person or at the home of a suspected assailant. 

It may be that it was suspected that the murder occurred after an argument fuelled by drugs and/or alcohol. Blood samples would then be taken at post mortem and sent to the forensic laboratory for forensic analysis for drugs and alcohol by a forensic toxicologist. The results of these analyses would then be interpreted by a forensic toxicology expert.


In a case of this type there could be several expert witness statements: from a forensic biologist, a forensic chemist, a fingerprint expert and a forensic toxicologist. The content of these statements may or may not be pulled together by an overarching statement from the ‘lead forensic scientist’ in the case. 


2. The crime scene of a large scale cannabis cultivation run by a serious organised crime group.


Drugs scenes of this nature are invariably ‘forensicated’ by police personnel (PCs and SOCOs - Scenes of Crime officers). Photographs are usually taken, cannabis plant samples are submitted to the forensic laboratory for forensic examination and forensic analysis and then usually the whole scene is dismantled and all the other cannabis plants are disposed of. This makes the job of a forensic drugs scientist quite problematic as they have to make their interpretation of the scene from photographs and the few sample cannabis plants submitted, with the rest of the forensic evidence having been destroyed.


The role of the forensic cannabis cultivation expert is to identify and analyse the cannabis plants submitted and, based on the photographs and police information about the crime scene to give opinions on the conditions under which the cannabis plants were grown and to estimate the potential yields of cannabis which could have been produced at the scene and ultimately sold. As the information available to the forensic drugs expert is limited, opinions of Crown and defence experts about potential yields can often vary and crucially depend on the levels of experience and expertise of the forensic experts involved. Cannabis cultivation on a large scale is usually a carefully controlled process as any deviation from optimum conditions could dramatically affect potential yields and the monetary value of a crop. It is important to assess plant yields properly as sentencing and asset seizure (under the proceeds of crime act) depend on crop value.


Established and experienced forensic drugs experts engaged by the defence may also be able to estimate crop values, based on their long-term knowledge of drugs markets and the different types of cannabis products sold in them. Original crop values are usually estimated by police ‘experts’.


There are occasions where a forensic cannabis cultivation expert will be asked to interpret a scene of a cannabis ‘factory’ and estimate yields from photographic evidence alone. 


3. The scene of a fatal Road traffic accident involving two vehicles


This type of scene may also need the expertise of forensic scientists from at least two forensic disciplines. 

A road traffic investigation expert can examine the scene and the vehicles involved to assess whether vehicle failure, climatic conditions or driver error or a combination of all three may have caused the fatal road traffic accident. In the case of a forensic defence expert they may have to interpret the scene from photographs and police reports, although the vehicles may still be available for forensic re-examination.


Blood samples would normally be taken from the deceased at post mortem and the surviving driver by a police surgeon, if possible. These blood samples would be sent to the forensic science laboratory to be analysed for drugs and alcohol by a forensic toxicologist, to see if either driver was under the influence of drugs or alcohol or both when the accident occurred. The role of a forensic toxicology expert witness is to assess the effects that any drugs and alcohol detected in the drivers of the vehicles may have had on their ability to drive at the time of the accident. 


Where the accident involves a ‘hit and run’ a forensic scientists specialising in chemistry may be asked to compare bits of broken vehicle component, such as a headlamp, found at the scene with a damaged component found on a vehicle believed to have been involved in the fatal collision.


4. The scene of an armed robbery where a firearm has been discharged


Scenes of this nature will involve a firearms and ballistics forensic scientist. The role of the forensic scientist and firearms expert may be to compare spent ammunition found at the crime scene with ammunition found in the possession of a suspect or to compare marks found on the spent ammunition with those made on ammunition fired from a recovered weapon in order to ascertain whether it is the weapon used in the armed robbery. 


There may be other evidence which requires the expertise of a forensic chemist who may be asked to compare shoeprints found at the scene with shoes worn by a suspect.


If the glass in a door or window is smashed to gain entry to the premises the forensic scientist specialising in forensic chemistry may also be asked to analyse and compare the glass from the scene with fragments of glass found on a suspects clothing.


A forensic fingerprint expert may also be needed to recover fingerprints left at the scene and compare them to those of potential suspects.



The statements of the Crown’s expert witnesses in cases like those previously described will be disclosed to the defence prior to the case going to trial. Defence solicitors may decide to engage one or more forensic defence experts to re-examine parts or all of the forensic evidence and decide whether or not the prosecution scientist’s investigations were carried out properly and whether they agree or disagree with the prosecutions version of events.  If the independent forensic scientists disagree they may offer alternative interpretations and opinions relating to the crime and the crime scene


This article just gives just a few examples of the roles that forensic scientists plays in the criminal justice system. There are many forensic disciplines, some covering broad topics like forensic biology and some very specialised like forensic entomology, but there are forensic scientists available to give expert opinion in all criminal cases and in cases involving all forensic evidence types.


If you are engaged in defending someone in a criminal case and you have evidence which requires appraisal by an experienced forensic expert witness then please do not hesitate to contact us. 


We will determine whether the forensic evidence can be challenged completely free of charge and will subsequently put together an estimate of costs for approval should you wish to have an independent forensic scientist comment on the forensic evidence against your client.


We have experts in a full range of forensic disciplines including amongst others drugs, drugs on money (POCA), drugs valuations, toxicology, drink diving, drugs driving, biology/DNA, blood pattern analysis, fingerprints, shoeprints, vehicle examination and firearms


Contact us today


Useful links
Find out more


Twitter feed

Stay connected

Subscribe to our newsletter.

Name* Email* Company