How Chemistry Uncovers Hidden Evidence in Forensic Science: From Lockhart's Principle to Cosmetics and Tires

Overview

In this lecture, Baljit Thatti of Kingston University presents how chemistry helps uncover invisible evidence in crime investigations. She introduces Lockhart's exchange principle, demonstrates transfer concepts with a beach ball and pepper, and delves into spectroscopy and chromatography as core forensic tools.

Through case-study sketches and applications to cosmetics and tires, the talk shows how trace components, dyes, dyes, soil and fabrics are analyzed to link suspects, victims and scenes. The talk also looks toward portable instruments and AI driven data analysis for faster, field-ready insights.

Introduction and Core Concepts

Baljit Thatti outlines the role of chemistry in forensic science, highlighting how even tiny traces can reveal crucial links between crime scenes, victims and suspects. Central to her talk is Lockhart's exchange principle, which states that every contact leaves a trace. A short demonstration with a beach ball illustrates how multiple people interact with an object and leave transfer traces such as fingerprints and hair.

She introduces the concept of the golden triangle, connecting the victim, suspect and crime scene, and emphasizes the need to separate signal from noise in complex samples. To illustrate how chemistry can extract meaningful information from apparently ordinary materials, Thatti compares sample analysis to tea making, where caffeine is the signal and other components are noise that must be managed by sensitive techniques like spectroscopy.

Techniques: Spectroscopy and Chromatography

The talk then surveys spectroscopy as a non-destructive way to interrogate evidence by how molecules absorb, transmit or reflect light. Infrared spectroscopy and near-infrared spectroscopy are highlighted as key methods, alongside chromatography for separating mixtures into individual components. A quick demonstration introduces thin layer chromatography as a simple illustration of separation principles that scale up to forensic analysis.

Thatti also discusses chromatography in the context of complex samples such as dyes in cosmetics, and the role of pyrolysis GC in analyzing rubber from tires. She explains how the resulting chromatograms provide chemical fingerprints that help identify brands and origins, despite the noise from the environment and substrates.