TOKYO — Surveillance footage showed the man entering a psychiatric clinic in a busy office building in Osaka, Japan’s third-largest city, and setting two large paper bags on the floor of the waiting area.
Within an instant, a fire ignited, ripping through the 270-square-foot clinic on Friday morning. By the time firefighters brought it under control, less than 30 minutes later, 28 people had been taken to a hospital. By the afternoon, 24 were confirmed to be dead.
On Sunday, the police put a name to the man, who they said was being investigated on suspicion of arson and murder. The suspect, Morio Tanimoto, 61, is in critical condition and has not been arrested, the police said. Two other survivors of the fire were also in critical condition on Sunday.
The fire, in a crowded district just steps from Osaka’s largest train station, rattled a country well known for its sense of security. It came just six weeks after another violent attack, in which the police said a man dressed as the Joker wounded 17 people with a knife on a Tokyo train and tried to set a fire onboard.
Last month, another man was arrested and charged with arson after a fire was set on a bullet train in Kyushu, in southern Japan.
According to the police in Osaka, street surveillance cameras captured footage of Mr. Tanimoto on a bicycle as he left his home less than three miles from the clinic, carrying two paper bags.
On Saturday, as rumors of the suspect’s identity emerged, journalists flocked to Nishiyodogawa, the neighborhood of nondescript beige and cream houses where Mr. Tanimoto lived.
Takehiro Kyoraku, an official in the investigation division of the Osaka prefectural police, said a small fire had occurred on the morning of the lethal fire at a home in Nishiyodogawa, though he would not confirm that it was Mr. Tanimoto’s residence. In the home, the police found a document indicating a relationship with the psychiatric clinic.
The fire raised questions about structural safety. The clinic, which specialized in internal medicine and psychiatry, was housed on the fourth floor of a narrow, eight-story building erected in 1970, which had just one stairwell. Fire safety experts say buildings should have at least two exits.
Over the weekend, according to NHK, Japan’s public broadcaster, the fire department in Osaka started urgent on-site inspections of buildings with only one set of stairs, identifying close to 5,500 such structures in the city of nearly 2.7 million. Fire officials were checking to make sure those exits were not blocked.
Two years ago, another arson fire at an anime studio in Kyoto, not far from Osaka, killed 33 people and injured dozens in one of Japan’s worst mass killings in decades. In that case, fire experts identified numerous problems with the building, which also had just one main stairwell and lacked fireproofing on interior fixtures.
Such incidents disrupt a fundamental sense of security in Japan, where crime is relatively scarce and the murder rate is among the lowest in the world.
“In Japan there is a myth of safety,” said Yasuyuki Deguchi, a criminal psychologist at Tokyo Mirai University. “Stopping these crimes is very, very difficult,” he added. “Most of these crimes occur without any warning. You cannot even guess that they are thinking about arson.”
Experts in arson say it is a public health issue, with many perpetrators showing signs of mental illness. Theresa A. Gannon, a professor of forensic psychology at the University of Kent in England, said that arsonists were often antisocial or had trouble forming intimate relationships, and that they used fire-setting as a coping mechanism or to get attention.
Ms. Gannon and a team at the University of Kent have developed a training program for mental health professionals to treat people who have a record of setting fires. She said that the team had trained professionals in the United States, Australia, Canada and Singapore and that a manual was available in Japanese.
Last year in Japan, there were nearly 2,500 incidents of arson, which killed 236 people, according to the Fire and Disaster Management Agency.