SAGAMIHARA, Japan >> Japanese police on Wednesday searched the home of the suspect in a mass stabbing spree that left 19 people dead at a facility for the mentally disabled.

Earlier in the day, suspect Satoshi Uematsu was transferred from a local police station to the prosecutor’s office in Yokohama.

Kanagawa prefectural authorities said the attacker left dead or injured nearly a third of the approximately 150 patients at the facility in a matter of 40 minutes. It was Japan’s deadliest mass killing in decades. The fire department said 25 were wounded, 20 of them seriously.

Uematsu, 26, turned himself into police early Tuesday, about two hours after the pre-dawn attack in Sagamaihara, a city about 50 kilometers (30 miles) west of central Tokyo.

He had delivered a letter to Parliament in February outlining the bloody plan and saying all disabled people should be put to death.

His head and shoulders hidden with a blue jacket, Uematsu was led out of a police station in Sagamihara and into the back of an unmarked white van with emergency lights on top. Photographers and video journalists swarmed the van as it pulled away.

At his house in Sagamihara police took in cardboard boxes to carry out any evidence. Parts of the property were sealed off with yellow police tape.

Security camera footage played on TV news programs showed a man driving up in a black car and carrying several knives to the Tsukui Yamayuri-en facility in Sagamihara, 50 kilometers (30 miles) west of Tokyo. The man broke in by shattering a window at 2:10 a.m. Tuesday, according to a prefectural health official, and then set about slashing the patients’ throats.

Sagamihara fire department official Kunio Takano said the attacker killed 10 women and nine men. The youngest was 19, the oldest 70.

Details of the attack, including whether the victims were asleep or otherwise helpless, were not immediately known. Kanagawa prefecture welfare division official Tatsuhisa Hirosue said many details weren’t clear.

Uematsu had worked at Tsukui Yamayuri-en, which means mountain lily garden, from 2012 until February, when he was let go. He knew the staffing would be down to just a handful in the wee hours of the morning, Japanese media reports said.

The facility employs more than 200 people, including part-timers, with nine of them working the night of the attack, Hirosue said. All those killed were patients.

“They were working at night and were questioned by police after witnessing graphic violence, making them a little emotionally unstable now,” he said.

In February, Uematsu tried to hand deliver a letter to Parliament’s lower house speaker that revealed his dark turmoil. It demanded that all disabled people be put to death through “a world that allows for mercy killing,” Kyodo news agency and TBS TV reported. The Parliament office also confirmed the letter.

Uematsu boasted in the letter that he had the ability to kill 470 disabled people in what he called was “a revolution,” and outlined an attack on two facilities, after which he said he will turn himself in. He also asked he be judged innocent on grounds of insanity, be given 500 million yen ($5 million) in aid and plastic surgery so he could lead a normal life afterward.

“My reasoning is that I may be able to revitalize the world economy and I thought it may be possible to prevent World War III,” the letter says.

The letter was delivered before Uematsu’s last day of work at the facility, but it was unclear whether the letter played a role in his firing, or even if his superiors had known about it.

The letter included Uematsu’s name, address and telephone number, and reports of his threats were relayed to local police where Uematsu lived, Kyodo said.

Mass killings are rare in Japan. Because of the country’s extremely strict gun-control laws, any attacker usually resorts to stabbings. In 2008, seven people were killed by a man who slammed a truck into a crowd of people in central Tokyo’s Akihabara electronics district and then stabbed passers-by.

In 2001, a man killed eight children and injured 13 others in a knife attack at an elementary school in the city of Osaka. The incident shocked Japan and led to increased security at schools.

This month, a man stabbed four people at a library in northeastern Japan, allegedly over their mishandling of his questions. No one was killed.

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Kageyama reported from Tokyo. Associated Press writers Satoshi Sugiyama and Ken Moritsugu in Tokyo contributed to this report.

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