無差別殺人犯罪：一種罕見而荒謬的暴力型態

Indiscriminate Homicide: A Rare and Peculiar Form of Violence

本文首先提出「無差別殺人」的定義，可分為廣義與狹義兩種，前者應至少符合兩客觀要件：一、兩造關係為單純陌生人者；二、須排除顯為財物、幫派、意識型態、現場一時情緒失控等因素導致之殺人事件。但因部分殺人案件動機難以辨識，僅能先排除多名加害人造成的殺人犯罪行為。另，狹義定義除前述兩要件，可再涵蓋兩客觀要件：一、犯罪地點需為公共場所；二、犯罪時間為日間。本文以2015年警方移送之故意殺人案件，估算臺灣無差別殺人案件盛行率為十萬分之0.11。因其他國家官方資料並無類似分類數字，故以各國陌生人殺人犯罪盛行率來比較。臺灣陌生人殺人盛行率是十萬分之0.25（含既遂與未遂案件），約同一時期美國陌生人殺人犯罪盛行率是十萬分之0.39（僅含既遂案件）、英格蘭／威爾斯是十萬分之0.22（僅含既遂案件）。本文將殺人案件分為四類：無差別殺人案件（A型）、多名加害人所為之陌生人殺人案件（B型）、家人或熟人殺人案件（C型）、混合了家人、熟人與陌生人的殺人案件（D型）。經統計比較後發現，無差別殺人案件更常發生於日間。嫌犯幾乎無女性；中壯年人（平均40歲）；多數有工作，且幾乎不可能是學生；殺人更常以刀器為主，少見鈍器或徒手者；犯罪情境中具有身心障礙或精神疾患約5％，因 不明因素殺人者比例更高；難以找到事前是否計畫之穩定模式。最後，本文討論以社會安全網來防治無差別殺人案件之發生，可 遭遇的險峻前途，以及所有的剖繪、評估預測、防治對策無非都是忽略小變數而來。為了本質而存在的無差別殺人事件，其偶發與荒謬性的本來面貌，終將被遺忘。

The present paper proposes the category of 'indiscriminate homicide'. In a broad sense, it is a form of violence (1) towards stranger/s and (2) without identifiable rational motivation or unknown circumstance. Apart from the two elements, in a narrow sense, it should include only homicides committed (1) in a public place and (2) during daytime. Based on the above tentative definition, this paper estimated the prevalence of indiscriminate homicide in Taiwan is about 0.11 per 100,000 inhabitants in 2015. It is rather difficult to find the similar estimation in other countries. However, we could compare the prevalence of stranger homicide as a proxy measure of indiscriminate homicide between countries. It is estimated that 0.25 per 100,000 for Taiwan (including attempt cases), 0.39 per 100,000 for the USA and 0.22 for the UK comparatively speaking for their prevalence of stranger homicide. By comparing four types of homicide, namely Type A indiscriminate homicide, Type B stranger homicide with specific gain, Type C domestic and acquaintance homicide, and Type D mixture of stranger, family and acquaintance homicide, the study finds that there are significant differences among these four groups. The indiscriminate homicide cases are more likely to be committed during daytime, about zero likelihood of involving a female perpetrator, average age 40, mostly employed in labor or service jobs, low educational attainment, primary method of killing by knife, 5% suffering from mental illness or disability, and half of them involving advance planning. The paper then discusses the prevention challenges that face development of an appropriate social security network against such a rare and peculiar violent event. To profile, assess, and intervene on indiscriminate homicide will require prioritizing a small number of important parameters. We must recognize that even when we embed our social security network, the inherent limits of any predictive knowledge means that some further homicides will not be prevented.