In 2003, when Kudo-kai reigned unchallenged in the city, 33.9 percent answered “yes” to the same question. The ratio had hovered around 2 percent since 2015.

On Aug. 24, the unprecedented death sentence handed down against the don of the Kudo-kai gang and the life sentence against its second-in-command is the culmination of that strategy. In 2012 ...