Toshihiko Hasegawa was born in 1950 in Japan and had three siblings. He was married with two children before the murders but later divorced. He owned a car repair business in Aichi Prefecture, which struggled financially, leading him into significant debt. In an attempt to alleviate his financial woes, Hasegawa devised a plan to murder individuals and collect life insurance payouts.

Between 1979 and 1983, Hasegawa and his accomplice, Masamichi Ida, committed three murders. 
Hasegawa took out a life insurance policy on Eguchi, a 20-year-old customer, and then drowned him during a fishing trip. However, Eguchi had left a suicide note, rendering the insurance claim void.
Hasegawa hired Harada as a truck driver and insured him for 20 million yen. Ida bludgeoned Harada to death, and they staged the scene as a traffic accident, successfully collecting the insurance money.
To avoid repaying a loan, Hasegawa and Ida murdered Sakakibara, a loan shark, by beating him and disposing of his body in the sea.

Hasegawa was arrested on December 25, 1983, and convicted on December 2, 1985. While on death row, he converted to Christianity and expressed remorse, writing over 150 letters to Masaharu Harada, the brother of one of his victims. Despite petitions for clemency from victims' families, Hasegawa was executed by hanging on December 27, 2001 .