A 50-year-old man who allegedly stabbed his 36-year-old coworker to death in a Tokyo law office Tuesday morning had harbored a long-standing grudge against the victim, according to investigators.

The attack occurred around 11:50 a.m. at the Adire law office at Sunshine 60, a high-rise in the Sunshine City commercial complex in the Ikebukuro area of Tokyo’s Toshima Ward.

Reito Watanabe is alleged to have approached Daiki Yoshino, a coworker from a different department, from behind while he was seated at his desk and stabbed him multiple times in the neck with a 9-centimeter folding knife.