I don't think it's been mentioned here yet, but the stabbing spree
occurred at a facility for the disabled; the BBC
clarifies that it was a facility for the mentally, not physically, disabled. Satoshi Uematsu is the name of the attacker. He actually worked at the facility until February.
The killer said that he wanted people with disabilities to disappear, so this was clearly an attack against the disabled. Obviously he's a psycho, but sadly Japan has some real problems with ableism. People with disabilities (both mental and physical) are often seen as drains on society, made worse by the fact that Japanese culture is very much about collectivism.