The alleged perpetrator of Tuesday's deadly knife rampage at a residential care facility for people with disabilities appears to have thoroughly planned the attack, bringing with him at least five knives, two hammers and other tools, investigative sources said Friday.

Satoshi Uematsu, a 26-year-old former worker at Tsukui Yamayuri En in Sagamihara, Kanagawa Prefecture, is believed to have carried a shoulder bag containing the weapons, as well as zip ties and gloves, at the time of the attack, they said.

Five workers were tied up in the massacre that lasted about 40 to 50 minutes and left 19 dead and 26 seriously injured, the sources said.