TOKYO — Japan was rocked by a horrific mass murder in Tokyo perpetrated by a 26-year-old man, Satoshi Uematsu, a former nursing home worker who stabbed to death 19 disabled residents and injured 25 others before turning himself into the police. It was the largest mass murder in Japan by an individual since the end of World War II. Yet, as horrible as the crime appears to be, it was not unprecedented.

There have been other similar killing sprees dating back to 1938. They share one common thread: motive. The famous prosecutor Toshiro Igari once said there were only three main reasons for murder in Japan, “Koi, Kane, Enkon.” The first two, Koi (love) and Kane (money) are universal but the third word, Enkon—is a complex thing—meaning hatred, envy, or a grudge. Enkon is such a powerful emotion in Japan that it is associated with ghosts, who are bound to this world because of their hatred. Enkon is the subject of a hit horror novel and movie in Japan that was remade in the U.S. as The Grudge in 2004.

This most recent mass murder shows all the signs of being one man taking his grudge against society out on the easiest victims he could find. And while Uematsu appears to want to portray his rampage as an act of “mercy killing” (he believes invalids should be put of their misery), it is more than likely just another young man with a seething grudge that boiled over into violence.