Nonaka told investigators that he was given the package by a man living in Phnom Penh soon after his arrival in the city two days previously. Authorities say they believe the operation was the work of an organised smuggling ring.

“Japan’s underworld groups are moving into different areas to bring in income, and one of those areas is getting older people involved in smuggling,” said Nagamoto Kuroda, managing director and head of forensics and litigation consulting for FTI Consulting in Tokyo.

As well as narcotics, older people are also being convinced to smuggle gold and counterfeit pharmaceuticals because they have in the past typically attracted less attention from customs officials, Kuroda said, although authorities appear to have caught on to this tactic.

Zachary Arnold, a 68-year-old American national, was arrested at Fukuoka Airport in December carrying about 10,000 tablets of ecstasy after arriving on a flight from France that had stopped off in South Korea. The haul, weighing in at 4.7kg and with an estimated street value of 40 million yen (US$381,680), was the largest ever seized at the airport.

Arnold told authorities that he “was simply told to carry the luggage” and had “no idea of what was inside”.

Jake Adelstein, a crime writer who specialises in Japan’s underworld groups, said the average age of Japan’s yakuza nowadays was about 50 “and they are not going to get their hands dirty doing this sort of thing themselves”.

“This is another example of what is termed ‘hinkon biz’, or a moneymaking scheme that preys on the elderly,” he said. “These are people who were in their 50s when the global recession struck in 2007, were laid off and were too old to get work again by the time the domestic economy had improved again.”

Elderly Japanese matching this description not only lost out on their expected future income “but they also were not able to pay into the national pension scheme, so the pensions they are getting now are often not enough to get by on,” Adelstein said.

The writer said it was “interesting” that Nonaka’s arrest was in Cambodia, where former yakuza kingpin Tadamasa Goto has based himself in recent years – though there is no evidence linking Goto to the case.

Hong Kong priest tries to save drug mules from system that favours kingpins

Smuggling gangs “do not care” when someone is arrested as they factor in such losses to their business model, Adelstein said, adding that courts in Japan have been more lenient towards older people caught smuggling, giving many suspended sentences rather than prison terms. If they are caught in other jurisdictions, however, judges have been less understanding.

“Smuggling drugs won’t bring in billions of yen for the yakuza, but it will certainly earn them in the millions, so it’s a reliable source of revenue when many of their other ‘businesses’ – such as protection rackets and illegal gambling – are increasingly becoming the target of the police,” he said.