Expert Evidence


Experts can be of great assistance to Magistrates and juries in aiding them to determine the issues in a case, including the guilt or innocence of an accused. Prosecutors will require the appropriate knowledge and understanding of the evidence in question to present and challenge expert evidence.

The purpose of this Guidance is to assist prosecutors in identifying, understanding and challenging, where appropriate, this type of evidence.

It should always be kept in mind that expert evidence is merely one tool to be used in proving a case. The danger in placing too much reliance on the findings of experts is demonstrated in a series of cases in relation to DNA analysis, where there was no other evidence against the accused save the presence of his DNA found at the scene of a crime. The Court of Appeal has emphasised that expert evidence can only be judged in the light of the other evidence in the case. In these cases, the absence of any other evidence, however limited, should have been fatal to the case being charged – see R v Doheny & Adams (1997) 1 Cr. App. R. 269 (at paragraph 372).

The dangers of an over-reliance on expert evidence without considering the significance of the other evidence in the case is a factor that prosecutors need to consider in reviewing any file presented by the police for advice and review.


There are various types of expert evidence, and many more new methods and mechanisms are being developed and applied everyday with the continuous advancement in science and technology. The currently available expert evidences are divided into the following types[4]:

  1. Medical Evidence- This type of expert evidence is given by a medical practitioner and it is conducted in a medical laboratory. These are further subdivided into the following types-
  1. Cause of Death in cases alleged to be due to physical violence;
  2. Cause of Death in cases alleged to be due to causes other than physical violence;
  3. Whether Death was accidental, suicidal or homicidal;
  4. To prove Legal Insanity;
  5. In cases of Sexual Offences;
  6. To determine age;
  7. In disputed Paternity cases; and
  8. Miscellaneous matters.
  9. Non-Medical Evidence- These are the expert evidences other than medical in nature. These are further sub-divided into-
  1. Fingerprints;
  2. Footprints;
  3. Handwriting;
  4. Typewriting;
  5. Forensic Ballistics;
  6. Narco-analysis;
  7. Polygraph Test; and
  8. Brain Mapping.

These are just some of the methods that are currently practiced in the investigation process in India. Many new methods and techniques are being developed and will soon be in use for the purpose of investigation, but in each method it must be ensured that the rights of the individual are not hampered. In cases where the rights of the accused are affected, the constitutionality of the evidence comes into question, which is further discussed in the next section of this research paper.

What Is The Evidentiary Value Of An Expert Opinion

The data given by the expert are relevant and admissible. If any oral evidence contradicts the data/ report; it will not make the data evidence obsolete. But, as per section 46, in case any fact is in contradiction to the opinion of the expert, that fact becomes relevant. If the opinion of the expert is relevant, the contradictory fact becomes relevant even though it was not relevant as such. The value of expert opinion depends upon the facts on which he is based and the competency of such expert in forming a reliable opinion.

However, the personal appearance of the expert in the court can be excused unless the court expressly asks him to appear in person. In such a case, where the expert is excused, he can send any responsible officer who is well versed with the facts of the case and the report and can address the court with the same.

If a judge relies upon the opinion of the expert only and not on the facts and the testimony of ordinary witnesses to give judgement then is the weakness of the case. This is because even if a person is an expert in his field, he cannot be termed as a direct witness and cannot give a statement on the facts of the case. He is just giving an opinion as per the evidences given to him and cannot draw a conclusion regarding the guilt of the accused in all the cases.


Unlike an ordinary witness, expert witnesses have a separate standing as a witness in a court. It is interesting to note that an expert’s report cannot be questioned in the court. The report is questioned when the ability and knowledge of the expert to make that report is in question. The experts are judged with a different eye by the court since they are just giving an opinion and are not aware of the facts of the case. But still, an expert’s opinion matters as the court has no knowledge of that particular field of expertise and they will not be able to impart justice without seeing the other side of the coin.

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