Chia Poh Ling, Lim T.B*, Chow Y.S, Lim Chin Chin, Michael Tay Ming Kiong
International Association of Forensic Sciences, 16th Triennial Meeting
August 2002, Montpellier, France, abstract No. PO-210 (poster presentation)
Objectives: This paper is a study of different cases involving the use or encounter of corrosive substances in crimes, suicides and accidents in Singapore in the past 6 years. It highlights the different techniques that have been successfully used to screen, detect, identify and characterise corrosive substances to address the questions and concerns of police investigators and the courts. It surveys the types of crimes, modus operandi, and types and sources of these corrosive substances. It illustrates how the geographical distributions of corrosive substances on garments and various articles can be used in reconstruction of the crime or accident.
Nature of study: The Singapore Corrosive Substances and Offensive Weapons Act provides penalties relating to the unlawful possession of corrosive and offensive weapons. This Act specifies nine corrosive substances, and includes all other substances capable on application to the human body of causing hurt through corrosive action. Chemical burns by corrosive substances, especially concentrated ones, are extremely painful. Injuries and scarring are often permanent, and deaths can result in attacks using corrosive substances. The extent of the injuries depends on the strength of the corrosive substance (reactivity and tendency to donate/accept protons or electrons), concentration, part of the human body exposed and exposure time. In the course of our work, we were called on to identify corrosive substances and their concentrations to help the court ascertain the facts of the case.
Materials and methods: This study is based on evidence submitted in more than 20 actual cases. A number of techniques were used: indicator papers, pH measurements, microchemical tests, scanning electron microscopy with energy-dispersive X-ray analysis (SEM/EDX), volumetric and gravimetric titrations, and gas chromatography with mass spectrometry. Mineral acids, organic acids and alkaline oxidising agents were encountered.
Results: Statistical results will be presented on more than 20 cases encountered in the past 6 years. Strong mineral acids and sodium hypochlorite solutions were most commonly encountered. In about a third of the cases, acids were splashed on the victim’s face and upper torso, sometimes resulting in serious injuries. Two tragic cases involved ingestion of concentrated mineral acids (sulphuric, hydrofluoric and phosphoric acids) by an infant and a 4-year boy, resulting in severe burns to the mouth and throat of the infant, and death in the boy.
Conclusion : Corrosive substance evidence may not be frequently encountered in crimes, suicides and accidents. Nonetheless the criminalist needs simple and reliable methods to identify and characterise them.