Tackling Crime through Science: ‘Every Contact leaves a Trace’ By Oluwatomi Ajayi

Tackling Crime through Science: ‘Every Contact leaves a Trace’ By Oluwatomi Ajayi

Crime is a major problem which threatens and destabilises the society. It is not therefore enough to simply affirm that society will be at peace mainly because the Laws are there to prohibit offences and prescribe punishments which deter potential offenders or perpetrators of crimes.

Apparently, more is required as the public is equally entitled to know an array of technology-based scientific process exists as evidence to solve crimes. Hence, science is playing a major role in the criminal justice all over the world.

For instance in Nigeria, the combined provisions of Sections 18(2) and 21(b) of the 1999 Constitution together with the 1993 Vienna Declaration and Programme of Action briefly encompass the terms, ‘Scientific Freedom’ and ‘Scientific Responsibility’ which the American Association for the Advancement of Science defined as the freedom to engage or pursue scientific knowledge and the corresponding duty to apply science with integrity in the interest of humanity.

In the sphere of criminal law, where science has an interface or nexus with crime scenes, crime investigation and crime detection which may require expert testimony in court of law or where natural sciences such as Physics, Chemistry, Biology, Geography, etc are used to analyse and evaluate physical evidence in court, then it is apt to refer such specialized field as Forensics.

The word Forensics was coined from the Latin term forensis which Black’s Law Dictionary define as ‘of or for the Courts.’ As an evidentiary aid which falls under the realm of science, Forensics is an application of science to solve legal disputes. It explores our living organism, made up of DNA which evidence is not visible to the naked eye but processed through biological instruments used to detect or examine genetic material from traces of sweat, saliva, skin cells, fingerprints, hair and other body parts.

These biological tools are CT-technology, microscopic examination, laboratory analysis, autopsy as well as from other ancillary aids identified by biometric samples, CCTV cameras, medical records or even a credible data obtained from statistical probability theories. Essentially, the aim of Forensic Science in crime investigation therefore is to identify perpetrators of criminal acts especially where at every point in time, direct evidence becomes controversial.

For example, memory of witnesses may fade or even fail. A witness can lie or die thereby reducing the quality of evidence. Thus comes the Locard’s Exchange Principle in Forensic Science which states that Every Contact leaves a Trace.”  

This crime solving principle attributed to the pioneer of Forensic Science Dr. Edmond Locard (1877 – 1966) submits that the perpetrator of a crime will bring something into the crime scene and leave with something from it.

This means that perpetrators of crimes leave their tracks on ground or traces of their activity in whatever they touch or wherever they go. For example, DNA evidence gleaned from a sweat sample from a lost shoe left at the scene of crime was held admissible by a court to convict a man for robbery. So was a man convicted for burglary and stealing based on fingerprint impression.

It should be noted that this discipline of Forensic Science exceeds the ordinary knowledge, skill, experience of the court where judges are mostly not grounded in science.

In this regard, an expert will be relevant to proffer a specialized scientific opinion in his specialized field in forensics whether in pathology, psychiatry, toxicology, odontology, computer, ballistics, linguistics, digital media and several other branches, done  in accordance with Section 68(1)& (2) of the Evidence Act 2011 which provides that when the court has to form an opinion upon a point of science, identity of handwriting or finger impressions, the opinions of persons specially skilled in science are admissible.

In a murder case for example, the advantage of Forensics is that it helps in developing profiles obtained from crime scenes. It aids in extracting usable or positive DNA analysis. There tends to be confidence in DNA science which harbours no sentiments, bias and prejudices. It holds a lot more information than eye witness or even confessional statements.

It enables a pattern of identification for those with no identity or those who use fictitious names. It has the capacity to reveal the genuineness of facts, better than a meticulous traditional detective work because detectives can get stuck. It can sieve out facts where there are suspicious circumstances.

Finally, Forensic science enables evidence to be preserved in the most original form. Suffice it to say that forensic evidence is an indirect or circumstantial form of evidence which the courts have held good and acceptable because according to them, witnesses may lie but circumstances capable of proving a fact with mathematics will not lie. Sabina Madu v. State (2007).

Obviously scientific evidence is not direct since the expert who will interpret the forensic evidence in court is not an eye witness in the first place. Moreover the evidence is also not visible to the naked eye because the testimony proffered by the expert will be secured from trace techniques.

Thus, the forensic science tendered in Court must satisfy the four validity tests as laid down in the case of Daubert v. Merrel Dow Pharmaceuticals (1993); namely peer review, error rate, standards and acceptance by relevant scientific community.

However, in the light of court judgements in Nigeria and other jurisdictions, courts are regarded as gatekeepers of science and therefore usually treat forensic evidence with caution making them to demand for additional evidence where necessary. In a decided case, it was held that a judge should have the discretion to dismiss inference made by expert if the expert goes beyond what was reasonable. This gives the Courts wide latitude to decide who and what to believe or not. In other words, who is an expert or his competence is a question for the courts.

In Harrison Odiawa v. FRN (2008), the appellate Court held that the trial Judge was right in rejecting the evidence of the appellant’s Police witness who did not give account of his skill and experience. Additionally, there are also a plethora of cases of cases which have shown why courts accept or reject scientific evidence.

Bearing in mind that criminals are getting smarter by the day, there should be a continuous engagement between forensic scientists and the relevant stakeholders in the criminal justice system such as the police, legal professionals and Judges.

All must work towards the objective behind Goal 16 of the 2030 Sustainable Development Goals (SDGs) which urges stakeholders to build capacity at all levels to combat crimes while one of the ways is to continue to explore science in crime investigation and for use in the courtrooms.


This Article was first published by the Lagos State Judiciary News in 2016 and written by Oluwatomi Ajayi, Chairperson, Research Committee of African Women Lawyers Association (AWLA) Nigeria and Author of ‘Crime Scene and Forensic Investigation; Basics of Tunnel Vision on Interrogation Process’  and ‘Simplified Criminal Law in Nigeria’ .


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