A man in his 20s stabbed at least 19 people to death at a facility for people with disabilities outside Tokyo. (The Washington Post)

At 1:37 a.m. Tuesday, security cameras recorded a black car entering a parking lot, then a man getting out of the vehicle and moving toward a building.

That was the start.

The man, apparently using his first-hand knowledge of the buildings that form the Tsukui Yamayuri-en residential center for the disabled, took a hammer and smashed a first-floor window. He then climbed inside, tied up some, maybe all, of the eight caregivers on duty, stole a set of keys and began a bloody rampage.

In the worst mass killing in Japan in about 80 years, the 26-year-old local man identified as Satoshi Uematsu went through the locked rooms of the care facility, where he had worked until February, and stabbed 45 people in less than an hour.

By the time he was done, 10 men and nine women would be dead or dying, and 26 would be injured. Twenty of those would be in critical condition, some with deep stab wounds to their necks.

He attacked people who could not respond to his questions, he would later reportedly tell police.

An emergency call was made at 2:37 a.m. — “something horrible is happening here,” the caller said — but the CCTV footage showed the man returning to his car before first responders arrived.

At 2:50 a.m., a tweet was sent from a Twitter account that appeared to belong to Uematsu. “Wishing for world peace. beautiful Japan!!!!!!,” it said, showing a photo of a smiling young man with dyed blond hair — the attacker’s hair was blond — and wearing a suit and tie.

A little after, Uematsu drove his badly dented black Honda sedan to the local police station and walked inside, carrying a bag containing three knives, at least one of which was covered in blood, according to local reports citing authorities.

“I did it,” he told police. “It’s better that disabled people disappear.”

He was arrested on suspicion of attempted murder and unlawful entry into a building.

By the time dawn broke over the lush green fields in this valley, 35 miles west of Tokyo, the residents of Sagamihara were left pondering questions that have plagued residents of cities such as Orlando, Nice and Munich.

Why did he do this? How could this happen? And here?

“This kind of incident is never heard of in Japan,” said Teruaki Sugimoto, 66, who lives near the care home, which is named “mountain lily garden” after the local flower that is in bloom at this time of year. A Ferris wheel on the hill behind the care center continued to turn. The air was punctuated by birdsong and announcements over police loudspeakers.

There were no quick answers.

Japan is a country with very little violent crime. There was only one gun death in this country of 127 million last year, and that was linked to yakuza gangs.

There have been occasional mass attacks, such as a 2008 incident in which a man in a truck plowed into a crowd of shoppers and then stabbed bystanders, killingseven. And the 1995 sarin gas attack on the Tokyo subway system by members of the Aum Shinrikyo cult, which killed 12 people.

But Tuesday’s rampage killed more people, becoming the worst mass killing in postwar Japan. The shock was compounded by the fact that it occurred at a care center where patients, many of whom were aged or bedridden, were completely defenseless.

About 149 people with physical and learning disabilities live at the center, and at least 30 of them had lived there for more than three decades.

The survivors remained in the care home after the attack, even after police hung blue tarp in the windows to keep out prying eyes. Moving the people would have been more disruptive than keeping them there throughout the investigation, authorities said.

The care-facility residents are a part of this small community. “We had lots of dealings with the residents during sports events and festivals,” Sugimoto said on his front doorstep. Other locals described seeing people in wheelchairs being taken for walks, or groups of residents going around picking up litter.

“As a community, we have been watching over the facility for decades,” said a woman who lived on the same street as Uematsu and gave only her surname, Enomoto. “It’s very quiet and peaceful here, so it’s a huge shock that it happened here and by someone we know.”

But there had been warnings of this dark day.

In February, Uematsu delivered a letter to the speaker of Japan’s House of Representatives in which he threatened to carry out an attack at this facility and through these very methods.

“I will carry out a massacre without harming the staff,” Uematsu wrote in the letter, copies of which were broadcast by local media. “I can kill 470 disabled people. My goal is a world where people with multiple disabilities can be euthanized with their guardians’ consent if it’s difficult for them to live at home or take part in social activities.”

Uematsu wrote that “I will carry it out at night time, when there are fewer staff on duty,” adding that he would tie up the staff who were at work.

A few days later, Uematsu told his colleagues that there was no point in seriously disabled people living, so they should be euthanized.

The colleagues alerted police, triggering a chain of events in which Uematsu was involuntarily committed to a psychiatric hospital, where he tested positive for marijuana use — a highly illegal substance in Japan — and was diagnosed as having drug-induced psychosis. Twelve days later, he was cleared for release, with doctors declaring that he no longer presented a threat.

Those decisions are facing new scrutiny. Five days after he delivered the letter, Uematsu stopped working at the care facility, but the details of his departure remain sketchy.

Prime Minister Shinzo Abe said his government “will do everything to get to the bottom of the truth.”

“I send condolences from my bottom of my heart to the many people who died and those who were seriously injured,” Abe told a political meeting on Tuesday morning.

For now, the residents of Sagamihara are going through a mourning process that looks starkly different from those seen at the sites of other mass killings around the world. There are no seas of flowers in front of the care center or public outpourings of grief.

“It’s unthinkable that something like this could happen, not just in Japan but here in our community,” said Mitsuo Kishi, 76, who lives a few hundred yards from Uematsu’s house. He stood at his gate and watched a steady stream of reporters filing past, telling those who stopped about the boy who lived down the road and wanted to be a teacher like his father.

“I'm speechless. I don’t know what to say,” Kishi said. “I still can’t understand why it happened here.”

Yuki Oda contributed to this report.