Reliability of Evidence and Biological Reality

The reliability of evidence concerns the extent to which evidence can safely
be relied upon in determining a disputed fact. Reliability is distinct from
mere relevance: evidence may be relevant to an issue while its reliability,
accuracy or weight remains open to examination.

In a criminal case, an evidential account may therefore be tested against
other evidence and against established physical circumstances. Where an
account depends upon a particular sequence of movements, positions, timing
or bodily actions, those assumptions form part of the factual proposition
that must be examined.

Evidence Must Be Tested, Not Merely Repeated

A factual proposition does not become reliable merely because it forms part
of a coherent narrative. The fact-finder must consider the evidence bearing
on the proposition and determine what weight, if any, it can properly carry.

In English criminal procedure, the court has an active role in ensuring that
evidence is properly addressed and that the issues in the case are identified
and dealt with fairly. The Criminal Procedure Rules expressly provide for
case management, disclosure and the treatment of expert, hearsay and other
forms of evidence.

When the Alleged Mechanism Matters

Where a case depends upon an alleged physical mechanism, the mechanism itself
may form an important part of the evidential question. The relevant inquiry
is whether the proposed sequence is consistent with the established
circumstances of the event.

This may include the relative positions of the persons involved, the location
and movement of objects, available space, timing, observable injuries and
other independently established physical facts.

A physical inconsistency does not automatically prove that an account is
false. It may, however, require the fact-finder to examine whether the
proposed explanation can properly account for the evidence.

Human Condition Is a Factual Variable

A person’s physical and cognitive condition at the relevant time may be
material to the reconstruction of an alleged event. Sleep, sudden awakening,
intoxication, injury, fatigue, medication and other physiological conditions
may affect the circumstances in which an event could have occurred.

Such factors should not be converted into unsupported assumptions about what
a particular individual was biologically capable or incapable of doing.
Where the issue depends upon medical or scientific expertise, the appropriate
evidential foundation is expert evidence rather than judicial speculation.

From Narrative to Reconstruction

A reliable evidential analysis should distinguish between what is directly
established, what is inferred, and what remains possible but unproven.

Where competing accounts require materially different physical sequences,
the relevant question is not which account sounds more natural. The question
is whether the evidence supports the proposed sequence and whether the
competing explanation has been properly considered.

Questions for Evidence Assessment

• What fact is the evidence being relied upon to establish?
• What part of that proposition is directly observed or independently established?
• What assumptions are required to connect the evidence to the alleged event?
• Is the proposed physical mechanism consistent with the established circumstances?
• Are biological or medical propositions supported by appropriate expertise?
• Are material inconsistencies between items of evidence expressly addressed?
• What alternative explanations remain consistent with the evidence?

Reliability is not the same as physical impossibility.

Evidence may be unreliable without being physically impossible, and a
physically difficult or unusual sequence is not necessarily impossible.
Physical impossibility is a separate and stronger proposition that requires
an evidential basis capable of supporting it.

The analytical discipline is therefore to identify the precise proposition
being tested, identify the evidence supporting or contradicting it, and avoid
converting an inference into a scientific conclusion without an adequate
foundation.

This page presents an academic analytical framework. It is not an assessment
of any particular criminal case.