Medical Expert Evidence under the Bharatiya Sakshya Adhiniyam, 2023: Scope, Limits and the Relationship with Ocular Evidence

Medical evidence is produced in almost every trial for an offence against the person, and it is the form of expert evidence most often misunderstood. It is frequently treated as though it settled what happened. It does not. A medical witness can say what injuries a body bears, what class of weapon could have produced them, and what caused death. He cannot say who inflicted them, and in the great majority of cases his opinion establishes possibility rather than certainty.

1. The Medical Witness

A medical witness gives evidence in two capacities at once, and keeping them apart is the beginning of any sensible analysis of his testimony.

As a witness of fact, he deposes to what he observed — the number of injuries, their situation on the body, their dimensions, their appearance, the internal findings on dissection. These are perceptions, and they are tested like any other perception: how carefully did he look, what were the conditions, what did he record at the time.

As an expert, he deposes to the inferences he draws from those observations — that an injury was caused by a blunt weapon, that death resulted from haemorrhage, that the injury was ante-mortem, that death occurred within a stated range of hours. These are opinions under Section 39, and they are tested by examining the criteria on which they rest.

2. What Medical Evidence Establishes

The scope of medical evidence in a criminal trial is wide but its limits are precise.

Cause of death. The medical officer states the immediate cause — haemorrhage, shock, asphyxia, poisoning — and where possible the sequence connecting it to the injuries found. This is ordinarily the most secure of his conclusions.

Nature and situation of injuries. Whether an injury is incised, lacerated, punctured, contused or a firearm wound; its position, dimensions and depth; whether it was ante-mortem or post-mortem; and whether it was sufficient in the ordinary course of nature to cause death, which is an ingredient of certain offences and is therefore frequently the critical opinion in the case.

The weapon. A medical witness can say what class of weapon could have caused an injury — sharp-edged, blunt, pointed, a firearm at a particular range. He cannot ordinarily say that a particular recovered weapon caused it, and an opinion expressed in those terms is going beyond what the discipline supports unless the injury bears some individualising feature.

Time of death. Estimated from rigor mortis, post-mortem lividity, cooling of the body, the state of decomposition and the condition of the stomach contents. Every one of these varies with temperature, humidity, the physical condition of the deceased and other factors, and a time of death is therefore always a range and never a point.

Other matters. Age of a person, the presence of poison, alcohol or drugs, the fitness of a declarant to make a dying declaration, and in sexual offences the presence of injuries and of biological material.

3. What Medical Evidence Does Not Establish

The limits matter as much as the scope, and three of them recur.

Medical evidence cannot identify the assailant. It has nothing to say about who inflicted an injury, and a case that rests on medical evidence with no evidence of identity is not a case at all.

Medical evidence cannot ordinarily establish that a particular weapon was used. It establishes that the injury is consistent with a weapon of a described class. Where the recovered weapon belongs to that class, the medical evidence corroborates; where it does not, the medical evidence contradicts. Neither amounts to identification of the instrument.

Medical evidence rarely establishes intention. It may support an inference — the site of the injury, its depth, the force required — but the mental element is drawn by the court from the whole of the circumstances, and a medical witness who offers an opinion on intention is going outside his field.

4. Medical Evidence and Ocular Evidence

The most litigated question about medical evidence is what happens when it does not fit what the eyewitnesses say. The principle is settled, and it is worth stating precisely because it is frequently stated loosely.

4.1 Applying the test

The question in every case is not whether the medical evidence differs from the ocular account, but whether it makes that account impossible. Discrepancies of the first kind are ordinary and are expected; discrepancies of the second kind are fatal.

The reason the threshold is set so high is that eyewitnesses and medical witnesses are describing different things. A witness describes an event as he perceived it under stress and in a short time; a doctor describes a body examined at leisure. Minor divergence between the two is the normal condition of a genuine case, and a perfect correspondence is more often a sign of a tutored account than of a truthful one.

5. Where Medical Evidence Is the Principal Evidence

In some classes of case there are no eyewitnesses at all, and the medical evidence carries much more of the weight. Three situations recur.

Poisoning cases turn almost entirely on the chemical examiner's report and the medical opinion on symptoms and cause of death. Even here, the medical evidence establishes that the deceased died of a particular poison; it does not establish who administered it, and the remaining circumstances — possession, opportunity, motive, conduct — must supply that.

Custodial death and death in a closed household frequently produce a case in which the medical evidence of injuries is the starting point and the burden then operates under Section 109, the facts being especially within the knowledge of those present. The medical evidence establishes that death was not natural; the absence of any explanation from those with exclusive access supplies the rest.

Sexual offences raise a particular question, because medical evidence of injury is frequently absent even where the offence occurred. The settled position is that the absence of injury is not proof that the offence did not take place, and a conviction may rest on the testimony of the prosecutrix where it inspires confidence.

The decision is reinforced by Section 48 of the Adhiniyam, which makes evidence of the character or previous sexual experience of a victim irrelevant in prosecutions for the specified sexual offences, and by the proviso to Section 149, which bars cross-examination of a prosecutrix as to her general immoral character or previous sexual experience on the question of consent.

6. Testing Medical Evidence

Cross-examination of a medical witness is directed at different targets depending on whether the point attacked is an observation or an opinion.

Where the target is an observation, the questions concern the examination itself — when it was conducted, in what conditions, whether the findings were recorded contemporaneously, whether the record is complete, whether anything was measured or merely estimated, and whether any finding was omitted.

Where the target is an opinion, the questions concern the reasoning — what criteria the discipline recognises, whether they were applied, what alternative explanations exist for the same findings, whether the literature supports the conclusion, and whether the witness is prepared to concede that the findings are consistent with more than one account. Section 40 makes the supporting or contradicting material relevant, and Section 45 makes the grounds of the opinion relevant, which is what permits this line of questioning at all.

The most productive line in practice is neither of these but the third: establishing what the medical evidence does not exclude. A doctor who concedes that the injuries are consistent with the defence version as well as the prosecution version has given the defence everything it needs, without any attack on his competence or his findings.

7. The Position Stated Shortly

1. A medical witness gives evidence in two capacities — as a witness of fact to what he observed, and as an expert to what he infers — and the two are tested differently.
2. Medical evidence establishes cause of death, the nature of injuries, the class of weapon, and an approximate time of death. It does not identify the assailant.
3. A time of death is always a range, and a discrepancy of some hours from the ocular account is not by itself a reasonable doubt.
4. Medical evidence is ordinarily corroborative. It proves that the injuries could have been caused as alleged, and nothing more.
5. It displaces ocular testimony only where it completely rules out the possibility of that testimony being true — total improbability, not mere inconsistency.
6. Minor divergence between the two is normal, and perfect correspondence is more often a sign of a tutored account than of a truthful one.
7. The absence of injury in a sexual offence is not proof that the offence did not occur, and the two-finger test is impermissible.
8. The most effective cross-examination establishes what the medical evidence does not exclude, rather than attacking the findings themselves.

8. Related Topics and Provisions