British tabloids were abuzz after a dramatic recent heist in London’s Hatton Garden diamond district, as thieves made off with more than £10 million ($15.5 million) in cash and gems from a heavily secured vault. According to one theory, the gang used a contortionist who slithered into the vault. Others held that a 30-something criminal genius known as the “King of Diamonds" had masterminded the caper.

But when police arrested nine suspects, the most striking thing about the crew wasn’t physical dexterity or villainous brilliance. It was age. The youngest suspect in the case is 42, and most are much older, including two men in their mid- seventies. At a preliminary hearing on 21 May, a 74-year-old suspect said he couldn’t understand a clerk’s questions because he was hard of hearing. A second suspect, 59, walked with a pronounced limp.

Young men still commit a disproportionate share of crimes in most countries. But crime rates among the elderly are rising in Britain and other European and Asian nations, adding a worrisome new dimension to the problem of aging populations.

South Korea reported this month that crimes committed by people 65 and over rose 12.2% from 2011 to 2013—including an eye-popping 40% increase in violent crime—outstripping a 9.6% rise in the country’s elderly population during the period. In Japan, crime by people over 65 more than doubled from 2003 to 2013, with elderly people accounting for more shoplifting than teenagers. In the Netherlands, a 2010 study found a sharp rise in arrests and incarceration of elderly people. And in London, police say that arrests of people 65 and over rose 10% from March 2009 to March 2014, even as arrests of under-65s fell 24%. The number of elderly British prison inmates has been rising at a rate more than three times that of the overall prison population for most of the past decade.

The US seems to have escaped the trend: According to the Bureau of Justice Statistics, the rate of elderly crime among people aged 55 to 65 has decreased since the 1980s. While the population of elderly prison inmates has grown, that mainly reflects longer sentences, especially for drug-related crimes.

Elderly people in developed countries tend to be “more assertive, less submissive, and more focused on individual social and economic needs" than earlier generations were, says Bas van Alphen, a psychology professor at the Free University of Brussels who has studied criminal behavior among the elderly. “When they see in their peer group that someone has much more money than they do, they are eager to get that," he says. Older people may also commit crimes because they feel isolated. “I had one patient who stole candies to handle the hours of loneliness every day," says van Alphen, who describes such behavior as “novelty-seeking."

Rising poverty rates among the elderly are being blamed in some countries. That’s the case in South Korea, where 45% of people over 65 live below the poverty line, the highest rate among the 30 developed countries belonging to the Organization for Economic Cooperation and Development. “The government should make an all-out effort to expand the social safety net and provide jobs and dwellings for the elderly," the Korea Times newspaper editorialized this month, warning that by 2026 more than 20% of the country’s population will be over 65.

The “Opa Bande" ("Grandpa Gang"), three German men in their sixties and seventies who were convicted in 2005 of robbing more than €1 million ($1.09 million) from 12 banks, testified at their trial that they were trying to top up their pension benefits. One defendant, Wilfried Ackermann, said he used his share to buy a farm where he could live because he was afraid of being put in a retirement home.

The perpetrators of the London jewel heist, though, were neither isolated nor impoverished. Prosecutors say the thieves disabled an elevator and climbed down the shaft, then used a high-powered drill to cut into the vault. Once inside, they removed valuables from 72 safe deposit boxes, hauling them away in bags and bins and loading them into a waiting van. Although their faces were obscured by hardhats and other headgear, the tabloids gave each thief a nickname based on distinctive characteristics seen on camera. Two of them, dubbed Tall Man and Old Man, “struggle to move a bin before they drag it outside," theMirror newspaper reported in its analysis of the security footage. “The Old Man leans on the bin, struggling for breath."

Most of the nine men charged in the case appeared to be ordinary blokes. The hard-of-hearing 74-year-old was described by his London neighbors as an affable retiree who loves dogs; the 59-year-old with a limp was said to be a former truck driver. Another defendant runs a plumbing business in the London suburbs. All nine are being held in custody on charges of conspiracy to commit burglary; they haven’t yet entered pleas.

Richard Hobbs, a sociologist at the University of Essex who studies crime in Britain, says the country’s criminal underworld has changed dramatically in recent years. Rather than congregating in pubs or on street corners, many criminals now live seemingly ordinary lives, raising families and running legitimate businesses. They still participate in crime, but only with trusted associates. “They don’t see themselves as criminals, they see themselves as businessmen," Hobbs says.

That makes it easier for elderly criminals to stay in the game. Older criminals often have extensive networks to draw on for needed expertise, Hobbs says. And some essential skills, such as money laundering, don’t require physical vigor.

Still, geriatric crime poses special challenges. During the trial of Germany’s “Grandpa Gang," the gang members described how their 74-year-old co-defendant, Rudolf Richter, almost botched a 2003 bank heist by slipping on a patch of ice, forcing them to take extra time to help him into the getaway car. And the 74-year-old had another problem, co-defendant Ackermann told the court: “We had to stop constantly so he could pee." Bloomberg