In March last year, Sato Kamiyama, 83, was nabbed - for the 28th time - for pickpocketing.

The serial criminal, now serving a jail term of 2½ years, had reportedly told the judge: "It's a bad thing to do to the victim. (But) I give up, it's hopeless."

Poverty did not seem to be a factor in this case. Kamiyama was living in an apartment in central Tokyo and could earn at least 260,000 yen (S$3,200) a month from renting out her other properties.

But it was a factor that had driven Tamako Sagai, 75, to crime. In May last year, she was arrested and charged with pickpocketing at least 20 other women for cash and items, in a spree that started in February 2015.

She would approach elderly women to ask for directions, using it as a distraction to steal from them.

"I did it for the money," said Sagai, whose case is pending and was reportedly living on welfare support.

These cases illustrate Japan's growing problem with geriatric jailbirds, whose numbers have continued to hit new highs, according to the latest crime statistics issued in November.

Observers have identified two reasons - alienation from society and poverty. While the overall crime rate dropped to a post-war low in 2015, the Justice Ministry highlighted the rise in offences committed by seniors.

In 2015, a record 47,632 elderly people, defined as those aged 65 and above, were arrested. More than 70 per cent of them were caught for petty crimes such as shoplifting. About 70 per cent of all the current inmates aged 65 or older are repeat offenders.

The issue led Japan's Diet to enact a law last month for national and local governments to implement measures to prevent recidivism,though the fine print is still up in the air.

National English daily Japan Times urged in an editorial last month for the authorities to "promptly work out measures to facilitate rehabilitation of these people who, in most cases, do not have a job or a place to live when they leave prison".

The new law comes as the country grapples with a rapidly greying population and a declining birth rate. By 2025, one in three citizens will be aged 65 or older and one in five, 75 or older. This has placed a strain on Japan's pension system, with some estimates showing that one in about five senior citizens today has an income below the poverty line.

It is against this backdrop that a prison in Asahikawa, Hokkaido, was recently refurbished to cater to more aged criminals in what is said to be the first such move in Japan. The average age of inmates at the prison is 50.6, with the oldest being 88, Kyodo news agency reported in November.

The prison can accommodate up to 500 inmates in private, well-lit cells, each with its own desk, chair, wooden bed and television set. Steps in public areas are equipped with ramps with handrails.

Poverty is one issue and market research firm Custom Products called Japanese prisons "state-sponsored retirement villages" in a report last year.

It said: "While much of it is petty crime, there seems a deliberate attempt to 'break into prison' as a way to survive. A roof over their heads, three square meals a day, no utility bills and unlimited free healthcare (are provided)."

Another issue is alienation, with more elderly people living alone. One in six senior citizens does so now, and observers like sociologist Emi Kataoka and senior administrator Yoh Satoh of newspaper Asahi Shimbun's Relife Project to promote active ageing stress the need to help the elderly improve their quality of life.

Mr Satoh said last month that one solution could be better social support, such as in the form of community centres to help the elderly socialise with one another.

As Dr Kataoka of the Komazawa University put it: "When a network of families and friends runs out, it is hard to live as an old man in Japan."