鄭捷（1993年－2016年5月10日），台灣新北市板橋區莊敬路人，高中畢業於板橋高級中學，是臺北「捷運殺人案」的主要兇手。這起案件因其血腥與規模，被視為台灣現代犯罪史上最嚴重的公共交通暴力事件之一。

鄭捷在學業上曾有不錯的成績表現，曾透過推甄考上台灣中正大學，但最終選擇就讀國防大學理工學院動力及系統工程系。然而，他在2013年6月因二分之一學分不及格而被退學，學業生涯首次受挫。之後，他於2013年9月參加轉學考，順利進入東海大學環境工程系二年級就讀，試圖重啟學業道路。

然而，學業上的波折未能改變他逐漸偏向極端的心理傾向。2014年5月21日，鄭捷攜帶鋒利的水果刀，在臺北捷運板南線龍山寺站與江翠站之間犯下駭人聽聞的殺人事件。據警方調查，他以平均每6.8秒造成一人死亡的速度，殘忍地殺害四名無辜乘客，另有二十多人受傷，造成整個社會震驚。這起案件因其高密度、極端暴力與公共場所作案的特性，迅速成為社會各界關注的焦點，並引發對公共交通安全與社會心理健康的廣泛討論。

案件審理期間，司法程式快速且嚴謹。2016年4月22日，法院正式判處鄭捷死刑。隨後，台灣法務部於5月10日接獲監察機關移交的案件卷宗，僅用七小時即完成審查，並交由法務部長羅瑩雪簽署死刑執行令。此一流程創下臺灣司法史上罕見紀錄：自判決定案到執行僅18天，審查及簽署程式僅耗時7小時，且僅執行單一死刑。此案不僅在社會上引發震撼，也成為台灣司法程式與死刑執行效率的一個重要案例，引發媒體、學界與社會各界長期的討論與反思。

Cheng Chieh (1993 – May 10, 2016) was a resident of Zhuangjing Road, Banqiao District, New Taipei City, Taiwan, and a high school graduate of Banqiao Senior High School. He was the main perpetrator of the infamous “Taipei Metro Massacre,” one of the most violent incidents in the history of public transportation in Taiwan.

Academically, Cheng initially showed promise. He was admitted to National Chung Cheng University through a recommendation program but ultimately chose to enroll in the College of Science and Technology at the National Defense University, majoring in Power and Systems Engineering. In June 2013, he was expelled due to failing half of his credits, marking his first major academic setback. Later, in September 2013, he passed the transfer examination and entered the second year of the Environmental Engineering program at Tunghai University, attempting to restart his academic path.

However, his academic struggles did not curb the escalation of his extreme psychological tendencies. On May 21, 2014, Cheng carried a sharp fruit knife and committed a horrifying attack on the Taipei Metro between Longshan Temple Station and Jiangcui Station on the Bannan Line. According to police investigations, he killed four innocent passengers at an average rate of one person every 6.8 seconds and injured more than twenty others, shocking the entire society. The case attracted nationwide attention due to its intensity, extreme violence, and the fact that it occurred in a public setting, prompting widespread discussion on public transportation safety and social mental health.

During the judicial process, the case proceeded quickly yet rigorously. On April 22, 2016, the court formally sentenced Cheng to death. Subsequently, on May 10, the Ministry of Justice received the case files transferred from the supervisory authorities and completed the review within just seven hours, after which Minister of Justice Luo Yingxue signed the death warrant. This procedure set a rare record in Taiwan’s judicial history: the death sentence was executed only 18 days after the verdict, the review and signing process took just seven hours, and only a single execution was carried out. The case not only shocked society but also became a significant reference point for discussions on Taiwan’s judicial procedures and the efficiency of death penalty enforcement, sparking long-term debate and reflection among media, academia, and the general public.