A DNA database match occurs when a profile obtained from a crime scene is compared with profiles stored in the national DNA database (NCIDD).

A match does not mean the circumstances of the allegation are proven. It means that the genetic profile obtained from the sample is consistent with a profile already recorded in the system.

The NCIDD Database holds samples from:

• Convicted persons
• Suspects of current crimes
• Forensic samples retained from earlier investigations
• Volunteers

If a match is obtained is an investigative lead only. If prosecution proceeds in reliance upon the database match, an evidentiary reference sample must be obtained from the person of interest.

A reference DNA sample is taken from an individual. This might be used for comparison with DNA recovered from a crime scene or item.

This is usually obtained through:

•  Buccal/mouth swab
•  Blood sample

The purpose is not to determine guilt, but to allow scientists to assess whether a person can be included or excluded as a contributor to the DNA profile.

The comparison is statistical and does not explain how the DNA came to be present

Crime scene work is inherently difficult to control for contamination and DNA transfer.

Handling at scene can lead to the courts excluding DNA where contamination is a concern.

Scenes may be compromised from earlier policing or paramedic activity.

In some jurisdictions, uniformed general duty police may be handling items at scene.

In other jurisdictions, highly trained CSI officers will be conducting such work.

The way a sample is collected, stored, and handled can influence what is ultimately detected. DNA can transfer between people and objects and be present from earlier contact.

Certain matters require a detailed review of crime scene logs, witness statements and BWC camera footage to assess DNA anticontamination procedures applied in the matter

In sexual assault matters, items such as clothing and bedding are most commonly sampled by police within their facilities.

Following this, the samples are sent to the DNA lab for testing.

The movements of the evidentiary items prior to the sampling counter are also important.

Frequently complainants provide clothing sometime after the alleged incident, which can be problematic for DNA testing. Any DNA upon those items may be transferred from one location to another during handling and packaging.

An evidentiary review of the sampling will consider the sampling officers contemporaneous notes, statement, relevant complainant statement and Crown Case Statement

It is commonplace for the complainant to be medically examined in a sexual assault.

This process seeks to obtain background information and biological material associated with the allegation.

The process typically uses a specially designed kit for collection of samples by the medical officer, and these are known by various names across Australia, including SAIK, FMEK, FECK, or rape kit.

Broadly, the medical examiner might take swabs of skin or genitals, including internal areas.

These procedures must be taken with the utmost care to avoid DNA transfer from one location to another.

A review of the medical sampling will consider the medical officers contemporaneous notes and statement.

iLaboratory testing involves extracting DNA from the samples and generating a DNA profile.

The DNA profile (or profiles) are then evaluated further.

Biological fluid samples may also be subjected to various testing protocols.

The DNA interpretation process is complex and may involve:

• Estimating the number of DNA contributors
• Consideration of differential extraction lysis
• Re-amplifying low level results
• Creating composite DNA profiles
• Comparing results to numerous ethnicity groups
• Interpreting partial profiles
• Running many statistical comparisons

In a typical matter, the DNA casefile generated is in the order of 200 pages (excluding the raw data).

nThe police investigative report is early evidence and might identify DNA and or body fluids.

The report information is used to target the investigation further and to support charges.

Body fluid results are often only presumptively tested and have not been confirmed by testing.

This report does not typically evidence the statistics (ie 100 billion times more likely).

Further DNA testing is often conducted after this report.

This report may describe:

• Where samples were collected
• Where DNA was identified
• Who the DNA might originate from

This report is not a scientific interpretation and is unverified. This report will essentially be replaced by a lab DNA report for trial.

gThe laboratory report summarises the scientific results.

This report may be served very close to the trial date.

Further supplementary reports may be evidenced.

The report typically includes:

• Whether the defendant can be included or excluded
• There will frequently be unknown DNA contributors listed
• The DNA likelihood ratio (ie 100 billion times more likely)
• Biological fluids testing results

The full laboratory casefile will contain information about subjective decisions and assumptions applied.

Commonly, there is other testing in the DNA casefile which is not in the report.

The DNA casefile is not usually provided with the lab report.

The matter cannot be reviewed scientifically without the DNA casefile.

DNA evidence will essentially form part of trial, unless it’s admissibility is challenged.

The courts refuse DNA evidence entirely more often than many people might assume.

Refusal is nuanced, but might be for numerous reasons including complexity.

Exclusion may occur where:

• DNA issues are too complex for a jury
• The DNA cannot resolve the evidentiary question
• The way the evidence is presented risks misunderstanding

The prospects of excluding DNA evidence in a particular matter are more closely aligned to the scientific elements.

Challenging the admissibility of the DNA evidence is both scientific and legal.

DNA is significant physical evidence, which might explain the allegation or another version

Studies acknowledge that jurors risk placing undue weight upon DNA evidence.

Undue weight can be increased where there is misunderstanding.

The court must be given DNA evidence that it understands.

The weight applied to DNA by the court depends on:

• Whether there are issues with the results
• How the interpretation is explained
• How the DNA evidence is explained
• How the DNA fits into background circumstances
• Whether the DNA results support the allegation or not

Where DNA is central, it must be handled with the greatest precision.