对一起交通肇事逃逸案件中死者衣服上油漆碎片与嫌疑车漆片的成分进行比对检验。红外光谱检验结果显示,死者衣服上沾有血迹区域提取的油漆碎片与其他部位提取的油漆碎片谱图有差异。对凝固的血迹进行检验,发现差异可能来自于血液污染。通过红外光谱差谱技术将血迹区域提取的油漆碎片的红外谱图进行处理,所得谱图与衣服上其他区域提取油漆的红外谱图无明显差异,证实死者衣服上只有一种油漆,且与嫌疑车漆片成分相同,这为证实嫌疑车的肇事事实提供了科学依据。

Paint evidence is usually encountered in hit-and-run accident. Transfer of trace paint occurs frequently in the striking process of the objects involved. It’s unavoidable that the paint smears are contaminated with environmental substances. Besides common contaminants, such as fibers, oils and dusts, the contamination may also come from blood or other materials. In order to achieve reliable conclusions, some countermeasures are required to recognize these interferences. This paper introduces a comparison examination of smeared paint samples from the victim’s clothes and the known paint chips of the suspected hit-and-run truck. Microscopic examination of physical features of the paint samples was performed with a stereomicroscope first; the organic components and elemental compositions were then analyzed with Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS), respectively. There were some spectral differences between the smears collected from the “bloodstain” area and those from the other area of the victim’s clothes. FT-IR results indicated that there were two possibilities: (1) the smears on the victim’s clothes might come from two different kinds of paint; and/or (2) the smears collected from the “bloodstain” area of the victim’s clothes might be contaminated by other substances. Contamination of the “bloodstain” area was not discernible with visual inspection. However, being aware that the sample could have been contaminated by blood, we examined a piece of known bloodstain by IR, it showed strong bands at 1658 cm^-1, 1544 cm^-1 and 1240 cm^-1 which were respectively attributed to the amide I, II and III, the typical absorption bands of protein. After software-enabled subtraction of the blood spectrum, the resultant spectrum of the smear sample collected from the “bloodstain” area showed no essential difference from those of the samples taken from the other areas, therefore, the smears collected from the victim’s clothes were supposed to be the same kind of paint. As the IR spectrums of the smears on the victim’s clothes and the paint from the suspected truck had no essential differences, combined with the results of SEM/EDS elemental analysis, the smears on the victim’s clothes very likely came from the suspected truck. The application of infrared spectral subtraction can help determine the chemical component of smeared samples.