The Reliability of Sampling to Measure the Weight of Seized Powder Containing Heroin

Abstract

Techniques used in forensic analysis have to find an appropriate balance between fairness to the defendant and efficiency and safety for forensic personnel. Safety issues are particularly acute in analyzing large seizures of bags likely containing heroin, possibly laced with fentanyl. National and local law specifies penalties that depend on the weight of seized powder containing heroin. Local custom makes available to the prosecution and the defense a preliminary report showing the presence of heroin and an indication of the powder weight seized. Such a report, even if it involves uncertainty, can be useful to both parties in understanding the likely sentencing range, with a view toward plea bargaining. An earlier methodological paper demonstrates how data from a sample of bags can be used to create a probability distribution for the weight of seized powder. The aim of this paper is to study whether sampling itself creates substantial additional uncertainty. To this end, we apply the above method to four populations with weights known for each item in the population. We draw eight random samples of size five from each population. Applying the proposed method to each sample, the results show that the variation created by drawing these samples is trivial. We conclude that the proposed method, which is convenient and safer for personnel, can be used without prejudice against the defendant.