Satoshi Uematsu, a former employee of the facility in Sagamihara west of Tokyo, stabbed 19 people to death on Tuesday, say police.
He had previously sent letters to politicians threatening to kill hundreds of disabled people.
The 26-year-old turned himself into police after the attack.
He was quoted by police as saying he had attacked those who were unable to communicate their feelings, broadcaster NHK reported.
There is a deep sense of distress that such a thing could happen here of all places, in this sleepy suburb nestling in quiet green mountains.
But that`s a discussion that is also taking place at a wider, national level.
Japan has one of the world`s lowest rates of violent crime. There were fewer murders in this country of 130 million people last year than there were in the city of Chicago, population less than three million.
Many reasons are cited: tough gun control laws; a communal culture that attaches deep shame to public acts of anger; low levels of drug abuse.
Japan is not immune to mass killings, but such events are rare, once a decade or so occurrences.
Could more have been done to prevent this latest crime? Should the warning signs have been more urgently acted upon? The question is, how much security is too much security in a country that, for the large part, doesn`t need it.
Japan knife attack: Suspect`s home searched by police
27 July 2016
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Police have searched the home of a man accused of carrying out Japan`s worst mass killing in decades, at a care home for people with mental disabilities.
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