Principle of Exchange and its Relevancy in Criminal

Locard’s principle of exchange was evolved in the early 19th century and it still plays an important role in tracing the evidence in a crime scene even with all development in technologies and equipment that are used to investigate  The Author has tried to explain the importance of Evidence in general and the significance of the principle in criminal law. Later on, trace evidence and its types are discussed. Finally, the criticism of the principle is discussed briefly, but the relevancy and importance of the principle in the present scenario and even in the future are put to thought later on.


The number of crimes happening in the world is ever-increasing and the need for stringent legislation and proper crime scene investigations are needed to identify the wrongdoer and the use of forensic and scientific evidence is used by the investigators to solve the crime puzzle as effectively and efficiently as they can. Although the manner and the way of investigation change with due course of time there are few basic principles and theories that will remain constant and one of it is the exchange principle of Locard which states that a criminal leaves behind a trace when committing a crime. The size does not matter and the investigator has to find the trace which is left by the criminal.

Importance of Evidence

Evidence is used to convict the criminals and it is found in the crime scene and the judges rely on the evidence obtained in the crime scene investigation and pass judgments after clear perusal of the same. Only when the evidence is put in front of the judge, the judge would be able to provide the judgment after looking into the pieces of evidence. One such type of evidence is Forensic Evidence obtained by scientific methods such as DNA, Blood tests, etc., and are usually used in courts to check whether the accused has done the crime. Forensic evidence is usually done by a team of experts and the tests are usually conducted in laboratories and they have such importance in today’s world of investigation. Locard’s Principle of Exchange is so relevant and plays a huge factor in Evidence and it is usually the role of the investigator to find out a clue and get evidence of the criminal. Many experts feel that as according to the theory, the trace left behind by the criminal might be Physical like Clothing or biological like a piece of Hair or Fingerprints but the trace is sure to be left behind and the investigator should find out the trace and the right criminal.

Principle of Exchange

Locard’s Principle of Exchange means when a criminal leaves a crime place, he would leave behind a trace consciously or unconsciously and the same will act as an Evidence against him and it usually acts as factual evidence and the same cannot be escaped, which leads to a saying that every contact by a criminal leaves behind a trace and the same will be evaluated by the forensic department and the results from laboratories will be easier to identify the criminal. The forensic department also helps to link crimes that have similar traces by the criminal or if they feel it is somewhat related to some other crime and this helps them to understand few traits of the criminal and filter down the suspects which would make it easier to find the criminal[1]. This eventually makes the life of the advocate to procure evidence to find the right criminal and for the judge to convict him and to maintain justice. Hence the Locard principle makes the forensic department to help justice prevail in the society and even today it plays an important role in finding out the right criminals.

Trace Evidence

Trace Evidence is something that is left by the criminal and which should be found by the investigators and the trace evidence can of any type – Hairs, Fingerprints, Glass, or any other natural shreds of evidence like Soil, etc., Where Hair or Fingerprints are common evidence that can be found in a crime scene and although if the criminal is careful enough the trace evidence should be there somewhere and nobody can escape from it. Forensic scientists usually break their heads to find some clue in a crime scene since now all criminals are careful in what they do but according to the Locard Principle of Exchange individual leaves behind a trace and the investigators must find out the break and the evidence which can be vital evidence to help convict the criminal[2]. The type of Trace evidence ranges from any physical evidence to single hair and the facilities have improved in such a way for the forensic scientists to filter the accused as per the evidence that was procured in the crime scene to detect the criminal.

The Trace Examiners use tools such as tweezers, specialized vacuums, lasers to find out the Trace evidence. When they know there should be some evidence as per this theory, the investigators would look deeply to procure that trace and check up on them later. Trace Evidence are the few basic things that are required to be taken by the investigators from the crime scene to start the case to find out the criminal as according to the trace, and it would be easy for the investigators if they find out a similar or the same trace evidence in two different crime scene and the same would help us to know the criminal through the trace evidence. Hence the trace evidence as per this principle plays an important role and a basic-criteria for this principle to work out and the same should be done by the crime scene investigators.

Criticism of Exchange Principle

The greatest drawback of Locard’s exchange theory lies in evidence dynamics. Criminal or anyone for that matter can change the physical evidence before it has been examined by investigators and criminals or accused who are interest party to a crime, can alter the evidence and even other things can alter the evidence which will go against this principle of exchange significantly and the results to find out a contact would not be a great result. Few factors that can lead to the destruction of evidence include Staging of evidence, Secondary transfer of evidence, the action of the victim before the crime, Witness actions, Natural factors like animal or insect activity, Actions of police, scene technicians, and medical personnel[3].

These factors can have a huge impact on the success rate of this principle and anyone – the criminal, witness, general public or natural factors can change the evidence by staging the fake evidence as per they want or transfer the secondary evidence or destroy the evidence that would help the investigator to find out the criminal. Any actions before the crime or the build-up before the crime which will not help to trace the contact but confuse the investigator.

Natural factors like animal or insect activity which might lead to change in evidence from its original place or any other change that can happen due to insects or any other natural factors which can have its impact on this theory. Tampering of evidence can also happen when the police officers, medical personnel, and the investigators come to investigate the crime scene and knowingly or unknowingly the evidence might have been missed by the investigators and other such people who come to investigate the crime scene. This principle works on the amount of evidence and the manner of evidence which had to be procured from the crime scene and one of the criticisms of this principle is that there are many factors which might change the evidence from its original form which will lead to finding wrong accused as criminals or not finding anyone at all.


Locard’s principle is significant and is very relevant in criminal law and most of the crime scene investigation works according to this principle and it does not lose its importance in criminal law and duty of the investigator to find out the trace left by the contact, with its size not being relevant. Though it has few drawbacks, it is logical for contact to leave a trace in the crime scene and biological evidence like DNA or fingerprints has more chances to leave its trace and the investigator has to find the trace to have its relevancy in criminal law even for the future like in the present scenario. A forensic team will have to update its way to examine the crime scene by using new methods because the evidence is tough to find in a crime scene every day. However, the Exchange Principle is the basic root of criminal law and will have its relevancy forever.



  1. What are evidence and its importance?
  2. What is Locard’s principle of Exchange?
  3. What is the significance of this principle?
  4. What is Trace evidence and its Types?
  5. What is the relevancy of Criminal law and the principle?

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