Abstract
BackgroundIn forensic science, age determination of bloodstains can be crucial in reconstructing crimes. Upon exiting the body, bloodstains transit from bright red to dark brown, which is attributed to oxidation of oxy-hemoglobin (HbO2) to met-hemoglobin (met-Hb) and hemichrome (HC). The fractions of HbO2, met-Hb and HC in a bloodstain can be used for age determination of bloodstains. In this study, we further analyze the conversion of HbO2 to met-Hb and HC, and determine the effect of temperature and humidity on the conversion rates.MethodologyThe fractions of HbO2, met-Hb and HC in a bloodstain, as determined by quantitative analysis of optical reflectance spectra (450–800 nm), were measured as function of age, temperature and humidity. Additionally, Optical Coherence Tomography around 1300 nm was used to confirm quantitative spectral analysis approach.ConclusionsThe oxidation rate of HbO2 in bloodstains is biphasic. At first, the oxidation of HbO2 is rapid, but slows down after a few hours. These oxidation rates are strongly temperature dependent. However, the oxidation of HbO2 seems to be independent of humidity, whereas the transition of met-Hb into HC strongly depends on humidity. Knowledge of these decay rates is indispensable for translating laboratory results into forensic practice, and to enable bloodstain age determination on the crime scene.
Highlights
Bloodstains at crime scenes have prominent forensic value
The oxidation of HbO2 seems to be independent of humidity, whereas the transition of met-Hb into HC strongly depends on humidity. Knowledge of these decay rates is indispensable for translating laboratory results into forensic practice, and to enable bloodstain age determination on the crime scene
No technique has yet shown the precision and reproducibility needed for age determination in forensic practice
Summary
Bloodstains at crime scenes have prominent forensic value. Techniques ranging from Atomic Force Microscopy [1], Electron Paramagnetic Resonance [2], and RNA degradation [3] have been explored to fulfill this omission. All these approaches confirm that the physical and chemical properties of bloodstains change over time. No technique has yet shown the precision and reproducibility needed for age determination in forensic practice. In forensic science, age determination of bloodstains can be crucial in reconstructing crimes. The fractions of HbO2, met-Hb and HC in a bloodstain can be used for age determination of bloodstains. We further analyze the conversion of HbO2 to met-Hb and HC, and determine the effect of temperature and humidity on the conversion rates
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