Technology is making armed robbery increasingly risky
Bank robbers may be the elite of the criminal fraternity, but over the decades the crime has become an increasingly risky one, offering less guarantee of ill-gotten gains than other forms of stealing such as internet hacking or white-collar fraud.
Increased CCTV, including camera programmes that can read the facial profile of those entering a bank, make the masked and armed demand for money an increasingly risky proposition.
Nowadays a bank is more likely to be separated from its money by computer hackers sitting behind a screen thousands of miles away.
Security expert Ian Hopkins, from firm Carratu International, sees it as significant that the raiders in the Belfast Northern Bank heist on Tuesday took two managers and their families hostage.
Mr Hopkins pointed out that straightforward shotgun robberies don't work any more.
He observed: "You can have all the locks and combinations in the world, but you can't eliminate the human element - that's the weakest link."
The security expert added: "Robbers could have problems getting rid of the cash.
"The bill serial numbers will not have been noted, but there's no point taking that amount of money unless you're going to spend it, and if you start spending it, it will be noticed."
He said bank operations will not be disrupted, with, at most, 48 hours of cash problems. Mr Hopkins also believed the insurance firms would pay up "without a murmur".
"One of the main problems for the bank going forward will be to reassure staff," he said.
John Henderson, who worked for the Northern Bank for 25 years, says the bank follows specific procedures.
"The one thing about banks is no one person has the authority to walk away with money.
"There is dual control in every situation, with two keys to open every door."
As well as the issue of serial numbers being potentially traced, many banks also have dye canisters that can be activated when cash is stolen.
The tactic of holding a bank employee is not a new one, but an indication of how harder it is to get away with a 'conventional' bank robbery.
In Manchester this autumn, a family was held hostage overnight as three men forced John Diggle, manager at Nat West in Whitefield on Bury New Road, to open the safe.
Mr Diggle and his family feared for their lives throughout this frightening experience, as the men made off with a "substantial amount" of cash from the branch, say police.
At the height of the Troubles banks in Northern Ireland were regularly robbed by paramilitary groups as a means of topping up their coffers.
The group with the biggest reputation for mounting bank robberies was the IRA, which in the past has gained access to high-security targets by taking the families of employees hostage.
Police in May accused it of taking staff hostage at Northern Ireland's biggest retail superstore, and stealing more than £4m in goods loaded onto a truck.
On this occasion police have said a well-organised criminal gang is involved, but they said it was "far too early" to say whether they had "any connections to a paramilitary group".
However, retired Northern Ireland police Special Branch head Bill Lowry said he suspected the Provisional IRA was involved.
"They have the capability, more than any other organisation, of carrying out this type of crime and dealing with £20m."