Tetsuya Shiroo was born in 1947 in Japan and became the leader of the Suishin-kai, a Nagasaki-based yakuza group affiliated with the powerful Yamaguchi-gumi syndicate. Little is publicly known about his early years, but by the 2000s, Shiroo had built a reputation within the criminal underworld and was known for his involvement in various organized crime activities. As head of Suishin-kai, he wielded considerable influence in the Nagasaki area, representing the interests of the Yamaguchi-gumi. Despite this position, there is no public record of violent acts attributed to him prior to the murder of Mayor Iccho Itoh.

On April 17, 2007, Tetsuya Shiroo approached Nagasaki Mayor Iccho Itoh outside his campaign office and shot him twice in the back with a revolver, fatally wounding him. Itoh died in the hospital the following morning. Investigators determined that Shiroo’s motive was a personal grudge against the mayor and city officials, primarily over the city’s refusal to pay compensation for a damaged yakuza-owned vehicle and the denial of a city contract to a construction company linked to his gang. Prior to the attack, Shiroo had mailed a letter outlining his complaints to a national TV station. He was quickly apprehended at the scene and later claimed that he intended to commit suicide after the shooting. Shiroo was indicted for murder, gun possession, and obstruction of election campaigning. He was originally sentenced to death on May 26, 2008, but on appeal, the Fukuoka High Court reduced his sentence to life imprisonment on September 29, 2009. Shiroo died at Osaka Medical Prison in 2020. After the killing, his gang, the Suishin-kai, announced its disbandment, and the murder was widely seen as an isolated act driven by personal motives rather than yakuza organizational orders.