Microbial Communities on Skin Leave Unique Traces at Crime Scenes

• NCJ Number: 252501
• Date Published: December 2018
• Length: 1 page
• Grant Number(s): 2014-R2-CX-K411; 2015-DN-BX-K430
• Agencies: NIJ
• Publication Type: Research (Applied/Empirical); Report (Grant Sponsored)

Annotation

This report summarizes the findings and methodologies of two related NIJ-funded studies that assessed the possibility of using an individual's skin microbiome (a community of microorganisms that inhabit a specific environment) as a form of trace evidence found at a crime scene.

Abstract

The first study examined whether the sequence in which surfaces are touched by an individual, along with the number of times the surfaces are touched, influences the detection of the person's microbiome. This study also considered whether an individual's skin microbial signature is recoverable from an object that had been touched by multiple people, as well as how long such signatures last on a surface. In addition, the researchers collected samples from deceased individuals at crime scenes and later collected samples from the bodies at morgues, so as to determine whether the signatures changed after death. The genetic signatures of these microbes were captured by swabbing and then extracting DNA from the bacteria in each of the samples. The 16s ribonucleic acide (RNA) gene was sequenced so comparisons could be made between bacteria from different samples. This study found that individual microbial signatures could be distinguished; however, the results were highly variable, based on the type of surfaces touched (plastic and ceramic surfaces yielded the best results), as well as how many times they had been touched (20 or 30 times gave the best results), with signatures lasting for at least 1 day. The second, follow-up study staged two mock residential burglaries to determine whether researchers could distinguish the burglars from the residents of the homes. The analysis showed that some samples could be traced to the possible burglar or entrant to the crime scene. This implies that extra caution should be taken to prevent crime-scene contamination by police, crime-scene personnel, and others.