Thieves copied one of the Home Alone film plots and pretended to be dummies when a department store was locked up for the night.
They got away with £10,000 worth of designer clothes after posing as mannequins alongside the real dummies on parade at Beales store in Worthing.
As soon as staff had gone and the store was empty, they ambled at leisure round the aisles picking out what they wanted.
Sussex Police were baffled as to how the gang, who are still on the run, got in or why they did not set off the alarm.
They got away with £10,000 worth of designer clothes after posing as mannequins alongside the real dummies on parade at Beales store in Worthing (pictured)
In Home Alone 2: Lost in New York, Harry Lime and Marv Merchants, played by Joe Pesci and Daniel Stern, hide out in Duncan's Toy Store on Christmas Eve
It only sounded when they left via a fire escape with thousands of pounds worth of designer clothes.
An assistant said the heist was a copy of Home Alone 2: Lost in New York, in which bad guys Harry and Marv plot to rob a toy store by hiding amongst the mannequins as it is locked up at night.
Beales is fitted with a sophisticated alarm system of sensors that should detect movement, and would have 'spotted' the burglars had they tried to break in.
'It was only triggered when they left the store - it was a very well-orchestrated crime' said the assistant, who asked not to be named.
'They must have secreted themselves and pretended to be mannequins.
'They probably dressed in clothes identical to those worn by the mannequins and stood there, not moving a muscle till the shop shut and everyone went home.
'They took oilskin jackets, high-end designer clothes and the like.
'It showed incredible nerve - the store is equipped from top to bottom with sensor alarms and cameras.
'They must have stood there with the mannequins not daring to move a muscle - imagine if they wanted to sneeze or had an itch they couldn't scratch!'
Harry, hiding in a toy house as they come up with the plan, says to Marv: 'Everybody leaves for a nice holiday'
A spokeswoman for Sussex Police said: 'We are investigating after the break-in was reported at Beales store in South Street.
'Clothing was stolen and the burglars left the store through the fire escape which set off the alarm. It is not clear how they got in.
'Officers are continuing to investigate. Anyone who saw anything or has any information is asked to contact police on 101 or on Crimestoppers anonymously.'
A Beales spokesman said: 'We do not wish to comment at this time.'
Pictured is Harry and Marv finding Kevin McCallister in Duncan's toy store in Home Alone 2
In Home Alone 2: Lost in New York, Harry Lime and Marv Merchants, played by Joe Pesci and Daniel Stern, hide out in Duncan's Toy Store on Christmas Eve.
Harry, hiding in a toy house as they come up with the plan, says to Marv: 'Everybody leaves for a nice holiday.
'We come out of our nice little houses, we empty the registers and then walk out like we own the joint.'
When they carry out the heist, Marv explains: 'We are fugitives of the law, we are up to our elbows in cash and there's nobody who even knows about it.'
But just as he says that, the film's hero Kevin McCallister, played by Macaulay Culkin, turns up and takes a picture before throwing a brick through the window to ruin their plot.