After rain caused deadly mudslides in Hiroshima Prefecture last month, rumors spread over the Internet about burglaries of evacuated homes by “foreigners,” including Zainichi (ethnic Korean residents of Japan). Such rumors tend to accompany disasters, so Tokyo Shimbun talked directly to police in the area.

There were six break-ins between Aug. 20 and 31, but the police had no idea of the nationalities of the burglars and seemed reluctant to say much else. The reporter spoke with residents of the stricken area and none said they had heard anything about foreigners looting homes except on the Internet.

He then spoke to several local Korean residents of the region, and all felt anxious about the rumors. As one woman said, “It is getting easier for people to post discriminatory messages” on the Internet. An expert on disasters told the paper that crime actually goes down after a calamity, but because of the attendant atmosphere of desperation and fear many people think otherwise, and thus “poisonous hearsay” flourishes more readily — in 2000, then-Tokyo Gov. Shintaro Ishihara told Japanese military personnel that foreigners could be expected to riot after a major earthquake. The expert added that these rumors reflect conventional thinking in the general population, and due to recent media coverage of anti-Korean sentiments the average person may believe them out of hand. It is thus important that authorities squelch such stories as soon as they emerge, something the police in Hiroshima did not do.

Tokyo Shimbun’s relatively extensive coverage of the issue was prompted by more than immediate events. The Hiroshima mudslides occurred just prior to the 91st anniversary of the Great Kanto Earthquake of Sept. 1, 1923. In the aftermath of that disaster, thousands were murdered after rumors spread that Koreans had poisoned wells and burned down houses. Some were killed by individuals, some by groups of vigilantes, some by civil or military police. Right-wing fringe groups deny there was a “genocide,” the term generally used to describe the killings, and there has never been a government investigation into the matter or an official expression of regret. It took place when the Korean Peninsula was under Japanese control, so the ethnic Koreans targeted were de facto Japanese nationals. Even the South Korean government never demanded acknowledgement of these crimes until local advocacy groups pressured it to demand that Japan identify the victims and apologize.

The 1923 killings were referenced by the U.N. Human Rights Committee in July when it recommended Japan ban hate speech against minority groups. Attorney Yasuko Morooka told Tokyo Shimbun that the committee was dismayed by the Japanese delegate’s response, which was that the murders were not relevant to the hate-speech discussion since they occurred before Japan ratified the U.N. Human Rights Charter in 1995. According to Morooka, by refusing to recognize past authorities’ complicity in mass killings of a targeted minority the current government inadvertently creates a “warm nest” in which anti-foreigner sentiment can grow.

The Sept. 1 issue of the Japanese-language version of the Korean daily Chosun Ilbo features an interview with Masao Nishizaki, a former school teacher who has dedicated his life to investigating the 1923 killings and making sure current and future generations of Japanese don’t forget they happened. He says that most Japanese history text books now don’t mention the killings and believes that without such knowledge it becomes more difficult to check the casual discrimination against Koreans that you find in social media.

“When I hear about hate speech,” he told the paper, “it reminds me of social circumstances in 1923.”

Those circumstances are described in a new book by Naoki Kato called “Kugatsu, Tokyo no Rojo de” (“September, On the Streets of Tokyo”), based on a now-defunct blog Kato wrote chronicling the day-by-day atrocities committed following the earthquake. Kato grew up in the Okubo district of Tokyo, where many Koreans live. While visiting the area last year he witnessed an anti-foreigner demonstration during which protesters yelled, “Kill Koreans.” He was researching the 1923 genocide and wondered how much things had changed in 90 years. He found dozens of eyewitness accounts in public and private records of Koreans being slaughtered on the street. In some cases, vigilantes attacked anyone who spoke with an accent, including people from other areas of Japan, thinking they were Koreans. He also read stories of Japanese people who risked their lives trying to protect Korean neighbors.

The perpetrators did not think of their victims as people. “They killed symbols,” Kato told Tokyo Shimbun in an interview last June. It had been more than 10 years since Japan annexed Korea and in the meantime an independence movement had developed on the peninsula. The Japanese kenpei (military police) violently suppressed it, which led to a violent response. Newspapers at the time characterized this response as being chaotic and vicious, and did not mention the cause, which was freedom from Japanese domination. More than a thousand Koreans were killed by police, but the media only reported the handful of Japanese civilians who were injured in the confrontations. The message was clear: Koreans were dangerous.

Kato thinks there isn’t much difference between 1923, when fear was generated by mass media, and 2014, when fear is generated by social media, since mass media isn’t doing anything to counter it. Tokyo Shimbun is a regional newspaper with limited reach. The more influential Asahi Shimbun, whose predecessor the Tokyo Asahi Shimbun spread anti-Korean propaganda in 1923, has in the past memorialized the lynching victims on Sept. 1, but not this year, probably because the paper is in the doghouse following its admission of misreporting the comfort-women story and may be sheepish about attracting more attention from right-wingers. The free press can also wind up a victim of hate speech.