Random killings occurred on the Bannan Line of the Taipei MRT, killing four and injuring 24.

On 21 May 2014, a Taiwanese man carried out a stabbing spree targeting random civilians on a Taipei Metro C321 train near Jiangzicui Station, resulting in four deaths and 24 injuries. It was the first fatal attack on the city's subway system since operations began in 1996. The attacker, 21-year-old Cheng Chieh, was arrested after the attack. He was sentenced to death, in addition to 144 years in prison, and was executed on 10 May 2016.

The Bannan or Blue line is a metro line of Taipei Metro in Taipei, Taiwan, with a total of 23 stations serving the districts of Nangang, Xinyi, Daan, Zhongshan, Wanhua, Banqiao and Tucheng. The line's name is a portmanteau of Banqiao and Nangang.

Taipei Metro is a rapid transit system operated by the Taipei Rapid Transit Corporation serving the capital Taipei and New Taipei City in Taiwan.

May 21 is the 141st day of the year in the Gregorian calendar; 224 days remain until the end of the year.