The target was a depot where a huge amount of cash - no one will say exactly how much - was being held awaiting distribution to Stockholm's ATM machines.
It looked like a commando operation. The helicopter had been stolen from a local airport. The thieves were lowered on ropes onto the roof of the building.
The few eyewitnesses said then heard the robbers blast their way in.
Police rushed in to set up a perimeter around a suspected robbery in progress.
Fearing the thieves were heavily armed, the first wave of police were instructed to wait for a SWAT team to arrive.
The crooks were way ahead of them, hauling their take and heading back into their waiting helicopter, making good on their escape. When police tried to get their their own helicopter in the air to pursue the robbers, they were foiled when they discovered a package reportedly labeled 'bomb' lying next to the aircraft they wanted to use. They decided not to risk it.
The thieves' helicopter was found abandoned some time later. The perpetrators had vanished along with the money. They left no trail, just a lot of embarrassed police, in their wake.
A reward of seven million Swedish Kronor - about a million dollars - has been offered for any leads to the crooks or the money.