A urine test conducted on the suspect in last month's deadly stabbing rampage at a care facility for the disabled in Sagamihara, Kanagawa Prefecture, tested positive for marijuana, investigative sources said Monday.

Police are investigating whether 26-year-old Satoshi Uematsu, a former employee at the Tsukui Yamayuri En facility, was high during the attack that killed 19 and injured 27, the sources said.

Uematsu, who originally refused to provide his urine, did not test positive for stimulants, they said.

The police have also determined that a small amount of plant matter found in Uematsu's home during a search in late July was marijuana.

He also tested positive for marijuana after he was committed to a mental hospital in February, and was diagnosed as suffering marijuana-induced psychosis. He was released in March because he was not diagnosed as an addict.

Uematsu is suspected of knifing residents to death at the care facility in the early hours of July 26 after breaking in by smashing a window on the ground floor.

He worked at the facility from December 2012 until February this year, when he quit after making alarming comments about euthanizing the disabled.