U.S. flag

An official website of the United States government, Department of Justice.

Evidential Value of Particle Combination Profiles on Common Items of Evidence

NCJ Number
Date Published
May 2017
22 pages
This project used the analytical tools and statistical methods developed in previous research funded by the U.S. Justice Department's National Institute of Justice (NIJ) to measure the evidential value of very small particle (VSP) profiles found on four common types of physical evidence: handguns, cell phones, drug packaging, and ski masks.

The previous research characterized VSP combinations using analytical instrumentation and expertise commonly available in forensic laboratories; developed statistically rigorous measurements of the strength of correspondence between VSP profiles; and measured the probative value of the resulting associations within well-defined experimental parameters. VSP were recovered from actual items of evidence: drug packaging, cell phones, handguns, and ski masks. The VSP were analyzed in an operational crime laboratory setting, using a practical, efficient analytical protocol. Under the experimental conditions, drug packaging showed excellent result for classification of test speciments (97 percent). Handguns and cell phones showed good classification results (90 percent and 87 percent, respectively). Ski masks showed poor results, with correction classification at 53 percent. Most misclassifications showed the correct source ranked remotely, indicating that these specimens did not have sufficient character to result in a strong association. VSP profiles on any given itemof evidence need not be complex and diagnostic. What is important is that on most they are unquestionably so. This finding encourages the follow-on research that will allow refinement and testing of the analytical and interpretational approach. 4 tables, 4 figures, and 10 references

Date Published: May 1, 2017