The rioters came from the very lowest level of Japanese society - day labourers who live from hand to mouth and whose existence is barely acknowledged in Japan.
Yesterday's newspapers and television news broadcasts largely ignored the riots and an officer at the local police station reacted angrily to inquiries from The Independent on Sunday.
The day labourers are outcasts from a society that stigmatises anyone who strays outside the norm. Some 20,000 live in flophouses and shabby dormitories in Airin, the largest slum in Japan. There are another 8,000 in Tokyo's Sanya district. They are seedy, run-down areas where crime is rife and the misery of unescapable poverty stalks the streets - a very different picture to most of Japan, which is comfortably middle class and relatively crime-free.
Some of the day labourers are criminals on the run or former prisoners who cannot get back into the mainstream of society. Many others belong to the burakumin (hamlet people) underclass, a group of people who are ethnically Japanese but who for centuries have been discriminated against because of their association with 'unclean' work - slaughtering animals, tanning leather and digging graves.
There are some three million burakumin in Japan, with the largest concentration around the Osaka area. Companies hiring new employees and families marrying off sons or daughters routinely use detectives to ensure they are not accepting a burakumin. In the past the burakumin were treated as absolute outcasts and their villages were not even marked on maps. Today they are similarly ignored by the media.
The riots began when the welfare centre in Airin announced on Thursday it would no longer hand out emergency welfare payments to labourers who could not find work. Most of the day labourers are employed in the building industry and queue up from 6 am to get a day's work. The process of recruiting is controlled by the yakuza, gangsters, who act as tough intermediaries between the workers and the building companies.
As Japan's economy is slowing, there are fewer new buildings going up. And because of the shortage of work, employers have begun to reduce wages. A day's work at the height of the economic boom five years ago could have brought in pounds 62. Today the daily wage is often barely half that, and with no official contracts or union protection, the day labourers have little bargaining power.
The local authorities had been making daily payments of pounds 9.50 to tide the workers over lean periods, but on Thursday they announced the funds for these payments had run out. Already living on the edge, the day labourers couldn't take it. A fistfight broke out between some of them and officials in the welfare office, and as news spread more people congregated outside, leading to clashes with the police. 'Day after day, we can't even get enough to eat,' one rioter told a local news organisation.
Two years ago Airin was the scene of five days of rioting after corrupt links between the local police and the yakuza were exposed. At least 186 people were injured, 55 were arrested and several hotels and a train station were burnt out.
Police further aggravated Airin residents when they installed video cameras on the streets, which were linked to the local police station to monitor any signs of unrest.