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Book Index - Charge: DNA Evidence

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[This charge is for use in cases where:

See Directions Under Jury Directions Act 2015 for information on when directions are required.

DNA evidence can raise a wide variety of issues in a criminal trial. This charge must therefore be substantially adapted in each case.

This charge is designed for cases where the likelihood ratio is expressed numerically. Where witness give evidence of the probability of a match using a qualitative scale such as "strong", "very strong" or "extremely strong", the judge will not need to warn against the prosecutor’s fallacy.

If the evidence exculpates the accused, or conflicting evidence is given by expert witnesses, it will need to be substantially modified. In such circumstances, General Principles of Opinion Evidence may provide some assistance.

This charge is designed to be used in conjunction with Charge: Uncontested Expert Evidence.]

Limitations of Evidence

Even if you accept NOW’s evidence, that does not necessarily mean that NOA must be guilty of the offence[s] charged. It is just one piece of circumstantial evidence, and must be considered in the light of the other evidence in the case. You will remember what I have told you about circumstantial evidence.[1]

It is important that you recognise the limitations of DNA evidence.

You will recall that NOW gave evidence that s/he tested the accused’s DNA sample and the [describe forensic DNA sample] at [state number of loci] loci, and that the accused’s DNA sample corresponded to the [describe crime scene DNA sample] at each of those loci.

People sometimes think that such evidence can prove who committed an offence. This is wrong. Evidence that NOA could not be excluded as the person responsible for [describe forensic DNA sample] only proves that NOA could have been the person who [describe relevant issue, e.g. "left the hair found on the deceased’s clothing"].[2]

As NOW told you, s/he only tested the samples at [state number of loci] loci. NOW could not rule out the possibility that the two samples would diverge if tested at other loci.

To address the possibility that someone else was responsible for the [describe the forensic sample], NOW also gave evidence about the probability of observing this DNA profile if the DNA came from a random member of the population who is not related to the accused. S/he said that the chance of this happening was [describe relevant ratio, e.g. "five million to one"].

This does not mean that NOA is [state relevant part of ratio, e.g. "five million"] times more likely to have committed the offence than a person chosen randomly. It simply means that roughly one person out of every [state relevant part of ratio, e.g. "five million"] has a DNA profile that matches the DNA in the [describe the forensic sample].

This means that, in a country the size of Australia, which has over 22 million people, there are likely to be [describe likely number of people in the population with a DNA match, e.g., "four or five"] people who could have been responsible for [describe the forensic sample].[3]

You must consider all of the evidence in this case, and decide whether it is possible that someone other than the accused could have been responsible for [describe the forensic sample].

[If the defence argues that the forensic sample may have been deposited in innocent circumstances or has been contaminated, add the following shaded section.]

The defence have argued that even if you accept that the [describe forensic sample] does contain NOA’s DNA, that does not prove that [describe prosecution inference, e.g. "NOA stabbed the deceased"]. This evidence will only be relevant if you find that NOA’s DNA came to be on [describe location of forensic sample] in incriminating circumstances and NOW could not give any evidence on that matter.

[Summarise and explain any prosecution and defence arguments in relation to the DNA evidence that have not yet been addressed.]



[1] If the judge has not given a direction on circumstantial evidence, this should be modified accordingly.

[2] This passage may need to be modified where the prosecution relies on DNA evidence as the sole or substantial evidence of guilt.

[3] If the population ratio is lower, it may be appropriate to state the number of people in Victoria who could be responsible for the evidence. In cases where the statistical evidence is especially weak, the judge might choose a smaller population group to use as the comparison, such as the number of other people at a football game. If the ratio is exceptionally high, such that statistically, NOA is likely to be the only person implicated, this section should be omitted.

Last updated: 29 June 2015

See Also

4.14.2 - DNA Evidence