From the story:
"He admitted that the post was false, but said he had seen claims that halal food had been provided in past disasters, which made him angry and led him to think, 'Why are Muslims given preferential treatment in Japan?'
'I posted this because I thought that this kind of thing would happen in the latest earthquake as well and that Muslims would be given preferential treatment,' he continued."
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Why isn't he being prosecuted for this? If the Yomiuri can find him, the police should be able to.