Tomohiro Kato killed seven people and injured ten others in the Akihabara electronics district of Tokyo on June 8, 2008. He was 25. The dead were aged between 19 and 74, and the case was later described as Japan's worst mass killing in seven years. He was arrested the same day, indicted in October 2008, pleaded guilty when his trial opened in January 2010, and was sentenced to death by the Tokyo District Court in March 2011. The Tokyo High Court rejected his appeal in September 2012, the Supreme Court dismissed his final appeal in February 2015, and on July 26, 2022 he was executed in Tokyo, at the age of 39.
His mental state was the main contested question. The defense argued that his responsibility was diminished or absent, and the Tokyo District Court found that he was fully responsible and had no mental disorder. The case also had effects beyond the courtroom: a pedestrian zone in the district stayed closed for two and a half years, and Japan tightened its rules on the possession of certain restricted items.
Akihabara is Tokyo's electronics and entertainment district, built around the railway station of the same name. On Sunday June 8, 2008 seven people lost their lives there and ten were injured. The seven who died were aged between 19 and 74.
Police arrested Kato on the day, on suspicion of attempted murder. He was 25. The formal indictment followed in October 2008, and he was charged with offenses that included murder.
The prosecution was brought in the Tokyo District Court. Because the case had been charged before Japan introduced its lay judge system in 2009, it was heard by three professional judges and not by a mixed panel.
The court set a schedule of 22 hearings between January 28 and August 4, 2010, with about 42 people, among them witnesses and bereaved and injured people, expected to testify. Two issues were identified in advance. The first was whether Kato had been mentally competent when he committed the offenses and, if so, to what degree he was responsible. Prosecutors relied on psychiatric examinations to argue that his responsibility was full; the defense was expected to argue that he was not competent, or that his capacity was diminished by a mental disorder. The second was whether it would be established that he had obstructed police officers carrying out their duties.
The trial opened on January 28, 2010. Kato, then 27, told the Tokyo District Court that he was the person responsible and pleaded guilty to the counts of murder and attempted murder. He also used the opportunity to apologize. The defense still maintained that his mental state at the time should reduce his responsibility, and that argument was the central contest in the case.
In court he said that he had acted because he had been the target of bullying on an internet bulletin board and wanted it to stop. He expressed remorse in court and in a letter to one of the injured.
In March 2011 the Tokyo District Court sentenced Kato to death. It determined that he had been mentally competent at the time of the offenses, and the finding was later summarized as full responsibility and no mental disorder. The presiding judge described the crime as "a brutal crime that did not show a shred of humanity on the part of the defendant" and said that death was "the only suitable punishment." Kato was 28 when the sentence was passed.
Kato appealed, and every later stage of the case was an appeal against a death sentence.
The Tokyo High Court rejected the appeal in September 2012. The case then went to the Supreme Court, which dismissed his appeal on Monday February 2, 2015 and found that there were no grounds for leniency. The death sentence became final that month.
After the sentence was final, Kato remained under it for seven years and five months. The Code of Criminal Procedure sets a deadline of six months from sentence to execution, a deadline that is almost never met in practice; between 2000 and July 2022 the interval from sentencing to execution ranged from one year to 19 years and five months.
Kato was executed on Tuesday July 26, 2022 in Tokyo, and the Justice Minister announced it. It was the first execution in Japan in 2022 and followed three in December 2021, which had ended a pause of about two years. The Justice Minister said that the sentence had been finalized through sufficient deliberation in court and that he had approved the execution only after the most careful review. He described the preparation for the crimes as "meticulous," said Kato had shown a "strong intent to kill," and called the case "an atrocious act that led to extremely serious consequences." He added that capital punishment remained a justified response to serious crimes, that abolishing it "wasn't appropriate at this point," and that mass killings and murders for gain continued to occur.
Japan then had 107 people under sentence of death, 61 of whom were seeking retrials.
At the time of Kato's execution Japan and the United States were the only Group of Seven nations that still carried out the death penalty, and a government survey found that an overwhelming majority of the public supported it. Executions are authorized individually by the Justice Minister. The Ministry of Justice has not explained how it chooses whom to execute, and the personal views of each minister have strongly influenced how many orders are signed. Prisoners are told of their execution on the morning it takes place.
Executions were not announced publicly until October 1998. In September 2007 the Justice Minister ordered that the names of those executed and the places be released as well, and since then Japan has disclosed the names and some details of the offenses, although the disclosure remains limited. From 2000 through July 26, 2022, 98 death sentences were carried out. Since the lay judge system was introduced in 2009, members of the public have taken part in decisions on capital punishment in the cases the new system covers; Kato's case was heard before that system applied.
The pedestrian zone in Akihabara, whose weekend event dated from 1973, was suspended after the killings. It was revived on a trial basis on January 23, 2011, after a district committee drew up a voluntary local agreement on cooperation and on safety and security. Japan also tightened its rules on the possession of certain restricted items.
On the 17th anniversary, in June 2025, people returned to Akihabara to pay their respects. One regular visitor said that the case was gradually being forgotten and that fewer bouquets were left at the site each year.
His mental state was the main disputed point. The defense maintained that his capacity was reduced; the Tokyo District Court rejected this and found full responsibility, and the higher courts upheld the sentence.
The reasons Kato gave for his conduct, including the bulletin board dispute, were his own account in court and were not adopted by the court as findings.
June 8, 2008: Seven people are killed and ten injured in Akihabara, Tokyo; Kato, aged 25, is arrested on suspicion of attempted murder.
October 2008: Kato is indicted on charges including murder.
January 28, 2010: The trial opens in the Tokyo District Court; Kato pleads guilty to the counts of murder and attempted murder.
January 23, 2011: The Akihabara pedestrian zone reopens on a trial basis.
March 2011: The Tokyo District Court sentences Kato to death.
September 2012: The Tokyo High Court rejects his appeal.
February 2, 2015: The Supreme Court dismisses his appeal; the sentence is final that month.
July 26, 2022: Kato is executed in Tokyo, aged 39.
June 2025: Mourners gather in Akihabara on the 17th anniversary.