An armed gang who stole at least £25m from a security depot in Kent held the manager and his family for more than six hours and threatened to kill them.
Police said the gang of at least six men had been "armed, dangerous, and violently threatening".
In what is thought to be Britain's biggest robbery, the manager, his family and 14 staff at Securitas were forced to co-operate during the raid.
The gang raided the depot in Tonbridge in the early hours of Wednesday.
Det Supt Paul Gladstone said the gang, some wearing masks and carrying handguns, had held the couple and their eight-year-old son in fear of their lives.
"We can be thankful that everyone was found unharmed," he said.
1: Security depot manager abducted near Stockbury
2: The man's wife and young son are taken from their home in the Herne Bay area
3: Armed and masked robbers raid the depot in Tonbridge
They first struck at about 1830 GMT on Tuesday on the A249 near Stockbury where the manager was abducted by men posing as police officers in a Volvo car.
Two further gang members, again posing as police, visited the manager's Herne Bay home telling his wife and son he had been involved in an accident.
The manager told police he was taken to a farm building somewhere in the West Kent area where he was held by his captors, and told to co-operate or his family would be in danger.
His wife and son were also taken to the same location at some stage during the night, and the manager was able to speak to them, before all three were taken to the Vale Road depot in Tonbridge at about 0100 GMT on Wednesday.
The raid was at Securitas' main cash depot south of the River Thames
Once there, the manager was forced to let one of the gang into the premises.
The robber then threatened a member of staff at gunpoint and forced him to open a gate to allow the remaining members of the gang to arrive in a number of vehicles.
All the staff were tied up and kept in a room along with the manager and his family while the money was loaded onto a white Renault 7.5-tonne lorry before the gang drove off at about 0215 GMT.
Staff at the depot have been conducting an audit to assess how much was taken, and are trying to establish the accuracy of claims that as much as £40m could have been stolen.
A mixture of new and used bank notes were stolen.
Ports and airports have been placed on alert in an attempt to prevent the gang from leaving the country with large sums of cash.
Mr Gladstone, of Kent Police's serious and organised crime unit, said the robbery had clearly been "meticulously planned".
"They [the gang] may have carried out surveillance at both the depot and followed the movements of the manager and his family," he said.
UK HISTORY OF ROBBERIES
December 2004 - £26.4m stolen from Northern Bank headquarters in Belfast
February 2002 - Thieves take $6.5m (£3.4m) from a British Airways van at Heathrow Airport
November 1983 - £26m in gold bullion and diamonds stolen from the Brinks-Mat high security vault, also at Heathrow
1963 - Armed robbers steal £2.6m in the Great Train Robbery
On Thursday, police were studying CCTV records from the site.
Mr Gladstone said: "I really want to know where the manager and his wife and son were taken after they were abducted and prior to the robbery taking place."
Detectives want to hear from anyone who saw:
The manager's silver Nissan Almera car being stopped on the A249 northbound, just past the Three Squirrels pub.
A Volvo or similar car rendezvous with a white van. Police believe the car joined the M20 at junction 7 and travelled westbound to junction 4 before taking the West Malling bypass.
The white 7.5-tonne lorry in the Tonbridge area in the early hours of Wednesday.
Anyone with any information is asked to contact an incident room on 01622 652361 or 01622 652366.