Semi-empirical Kinetics Model for Fingerprint Aging

Fingerprint analysis is the first tool of choice in the forensic identification toolbox with more than 100,000 searches per day in the FBI database. However, there is no reliable method to determine the time-since-deposition (TSD) of latent fingerprints, resulting in the need to rely on eyewitness accounts or surveillance systems to link a suspect to the crime scene location at the time of the crime. Establishing alibis and verifying eye-witness accounts can be very time-consuming for law enforcement, which drives the need for a reliable way to estimate when a fingerprint was deposited at a crime scene. The researchers at Iowa State University propose the development of a semi-empirical kinetics model for fingerprint aging. The purpose of this proposal is to rigorously determine the TSD of fingerprints collected from the crime scene based on the fundamental principles governing chemical kinetics.  It has been shown that the ambient ozonolysis of unsaturated triacylglycerols (TG) and other fingerprint lipids is the main mechanism of fingerprint aging. Expanding on the partial success of the previous simple pseudo-first-order kinetics model, the semi-empirical kinetics model can explain not only the temperature and ozone concentration dependence in the TG decay over time but also the person-to-person variability from the difference in fingerprint lipid profiles. 

A mass spectrometry-based analysis, called matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS), will be used to measure the relative abundance of these fingerprint lipids and their change over time. The resulting datasets will be used to derive kinetics parameters that can be applicable to any aged fingerprints at a given temperature and ozone concentration. First, the apparent activation energy will be deduced from the in-depth study with a small sample population as the person-independent molecular parameter. Then, a large-scale population study will be performed to determine the association between the fingerprint lipid profile and the frequency factor associated with the reaction kinetics. Finally, the established model will be tested and validated in a set of forensically relevant mock experiments. Multiple manuscripts and presentations at national conferences are expected to disseminate these findings to the forensic science communities, in addition to publishing the data collected in an appropriate repository. At the end of this project, an advanced kinetics model will be developed that will be ready for validation in real forensic applications. CA/NCF