At 70, Yasumasa Matsuzaki did not look especially dangerous. He was just a nuisance to the workers at a convenience store because of his habit of reading magazines without ever buying anything.
So after one marathon three-hour session, the manager of the shop in Bando, Ibaraki Prefecture, snapped and threw him out.
Five minutes later, Mr Matsuzaki returned with a chainsaw and threatened the staff before returning to the magazine rack.
"He was absorbed in reading even after we called the police," said the manager after Mr Matsuzaki had been charged with forcible disruption of business. "He was very scary."
The incident last week is part of a wave of so-called grey crime in Japan. The percentage of over-65s in prison has trebled in the past decade and exceeds 10 per cent of the total prison population - four times the UK figure. Japan has the highest rate of incarceration for pensioners in the industrialised world.
While most are in prison for theft, there are a number of convictions for violent crime. Among the 141 pensioners arrested for murder last year were an 81-year-old man who strangled his spouse after they bickered over her cooking and an 87-year-old man who strangled his bed-ridden wife in a hospital in Nagano.
Many offenders will end up at Onomichi prison in Hiroshima, a special facility for elderly prisoners equipped with handrails, pushcarts and walking aids. The inmates include a pensioner who beat up his care worker after he threatened to resign and an elderly married couple who held up a convenience store.
More than 80 per cent will return within a year of release. "There are not too many companies that will hire an 83-year-old ex-con," one former inmate recently told a weekly magazine.
"Prison in Japan is becoming a place for the old and the disabled who have slipped through the cracks of the welfare system," said a former politician, Joji Yamamoto, who was "outraged" by what he saw behind bars after being convicted of fraud. "Many end up dying on the streets or committing another crime and landing back in jail."
The Japanese Justice Ministry is so alarmed by the rise in geriatric crime that it has started a research project into its causes. Police departments have devised questionnaires for elderly prisoners in an attempt to find out what makes them tick. Among the factors they are exploring are fear of the future, poverty and loneliness. "We have no idea what is causing the rise in the elderly crime rate," said Yoshihiro Ono, a ministry of justice researcher.
Some commentators say there is no mystery. In addition to having the world's longest life expectancy at 85 for women and 78 for men, Japan's welfare system is struggling with a rising pension burden. Nearly nine million elderly people live on pensions, of which just under half are less than 40,000 yen (£194) a month.
The pressure of poverty, the burden of caring for infirm spouses and the lack of professional back-up appear to be driving some to crime and the government has been slow to move on an issue involving welfare.
In the meantime, some people are taking the law into their own hands. When a man described by police as "in his eighties" broke into a Tokyo home and stole 50,000 yen, he was confronted by the female owner who fended him off with a glass ashtray. "I tried as best I could to strike back," said the woman, who was 79.Reuse content