骨質刀痕角度與刀器角度鑑識之生物動力學研究

Abstract

刀器造成受害者的銳器傷向來是他殺案件的主要來源，當銳器傷及人體骨骼，必留下工具痕跡，成為刑事偵查案中探討工具痕跡證據為鑑識科學主要課題。本研究將收集2005至2009年間之法醫相驗解剖之他殺案件與外傷中銳器傷案件，回溯性篩檢來瞭解台灣地區銳器傷相關的流行病學研究。而銳器傷的型態有砍傷、刺剪傷、切割傷、穿刺傷等；在刀痕工具痕跡方面，本研究的銳器傷對象以砍傷為主，透過生物動力學研究，以羊腿骨模擬骨質刀痕角度，發展生體工具痕跡鑑識技術，並建構人體刀傷與刀器比對鑑驗之標準作業流程。 本研究利用不同施力來產生撞擊動量(質量•速度)之物理性質，製作刀器工具痕跡砍劈實驗模擬平台，透過高解析3D立體顯微鏡掃描量測刀痕工具痕跡角度。骨質回彈係數（κ）為刀器刀刃角度（θ）與骨質刀痕角度（φ）之比值，顯示骨頭受刀器砍劈後彈性恢復之程度，藉以探討分析刀器、骨頭在撞擊時之生物動力學與刀器及工具痕跡之關係。 本實驗結果顯示，骨質刀痕角度（φ）與撞擊動量有正相關性。在固定刀器重量條件下，調整刀器分別於9.8至49.0公分（其中墜落高度依重力加速度G=9.8m/s2之簡單倍數）高處落下，發現骨質刀痕角度（φ）介於10.66±0.29度至38.32±0.33度，計算其骨質回彈係數（κ）介於1.16±0.03至2.70±0.06，當撞擊動量愈大而骨質回彈係數（κ）亦愈大，且雙鋒刀刃類之骨質回彈係數（κ）與撞擊動呈較佳之線性關係，而偏鋒刀刃類之骨質回彈係數（κ）與撞擊動量也有骨質回彈係數（κ）隨撞擊動量增加而變大之趨勢。本研究顯示台灣地區2005至2009年間，法醫相驗解剖死亡案件中他殺案件共有1120件中，銳器傷就佔349件（31.16%），與死亡年齡統計中以25-44歲之青壯年人為他殺案件中銳器傷最多數（佔198件、49.25%），銳器傷致死與性別統計顯示男性佔比例較高〈佔279件、69.4%〉。刀器工具痕跡與生物動力學實驗方面，利用高解析3D立體顯微鏡技術來量測刀器工具痕跡並將其實驗結果統計來建立刀器骨質動力學等研究資料庫，並利用骨質彈性係數和撞擊動量之線性關係，還原凶手犯案時可能之施力大小與方式，最後建構人體骨質刀痕與刀器比對鑑驗之標準作業流程，提昇國內法醫刑事鑑識有關骨質刀痕生體工具痕跡比對的鑑識能力。

Sharp instrument injury by knife becomes the leading cause of homicide in Taiwan. According to 1910 Edmund Locard’s Principe, the tool marks can play a crucial role to profile the shape, nature and characteristics of weapons. Therefore, the study of tool mark is one of the major issues in forensic investigation of criminal cases for identifying and mapping the tool mark on bone tissue. Retrospective study of sharp-instrument injury-related homicide cases during 2005~2009 is conducted. Sharp instrument injuries include chopping wounds, stab wounds, cutting wounds, and penetrating wounds. Through biomechanical studies, lamb bone was used to simulate the human bone under sharp tool chopping, so as to develop the mapping technique and to correlate the sharp instrument impacted on bones, and so as to establish the standard operation procedure for identifying the sharp instrument in correlative with chopping wound on bones. In this research, the experimental chopping stage is designed for knife tool marks. With different impulsive forces generated by angular momentum (velocity and mass) of the knife, different knife tool marks would be observed by 3D digital microscope. The ratio between the knife angle(θ), and the V-shape tool mark angle(ψ), is assigned as κ value (elastic coefficient : θ/ψ) to represent the degree of elastic rebound after the impact of the knife on the bone. The experiment result reveals the V-shape knife tool mark angle is proportionally related to the impulsive force. Under fixed knife masses, with different falling height of the knife (form 9.8cm to 49 cm) were used to mimic the impact force. V-shape knife tool mark angles and the elastic coefficient were 10.66±0.29 to 38.32±0.33 degrees and 1.16±0.03 to 2.70±0.06, respectively. The greater the angular momentum of the knife chopping induces a larger the elastic coefficient of bone. Besides, the double-edge knives induced the V-shape knife mark angle demonstrate a linear relationship between the elastic coefficient and the angular momentum. 349 out of 1120 homicide-related autopsy cases were the sharp instrument-related victims. High risk age ranged between the age of 25 to 44 years old. In conclusion, these results data from the biomechanical and epidemiological studies could be compiled into a practical use for the strategy for the forensic examination and benefit to the identification for knife tool marks, so as to promote the credibility in medico-legal investigation in Taiwan.