Establishing likelihood ratios for evaluating opposing propositions concerning the activity causing methamphetamine...

Area of Science:

• Forensic Chemistry
• Environmental Science
• Law

Background:

• Methamphetamine contamination in New Zealand households is a growing concern, particularly when the source is unknown.
• Determining the origin of methamphetamine residues is crucial for legal cases, such as "Use of Premises" charges under the Misuse of Drugs Act 1975.
• Current analytical techniques lack the ability to definitively determine the provenance of methamphetamine residues.

Purpose of the Study:

• To develop a method for distinguishing between methamphetamine contamination resulting from manufacturing versus drug use.
• To provide a scientific basis for evaluating evidence in clandestine laboratory cases.
• To introduce a novel Bayesian approach for interpreting forensic evidence related to methamphetamine.

Main Methods:

• Collected and analyzed data on methamphetamine contamination levels from suspected clandestine laboratories (manufacturing) and properties where drug use was suspected.
• Modeled likelihood ratios (LR) by comparing contamination levels between the two scenarios.
• Utilized established Bayesian statistical principles for forensic evidence interpretation.

Main Results:

• Established distinct contamination level profiles for methamphetamine manufacturing versus drug use.
• Quantified the likelihood ratios (LR) associated with different contamination levels.
• Demonstrated the potential for a data-driven approach to provenance determination.

Conclusions:

• The developed model, based on likelihood ratios, can aid in differentiating the source of methamphetamine contamination.
• This research provides a foundation for a novel Bayesian framework in evaluating clandestine laboratory evidence.
• The findings have significant implications for the New Zealand legal system concerning drug-related premises charges.