Robbers fly in by helicopter to raid Swedish cash depot

Explosives left at police hangar to stop officers flying to the scene of the crime

Masked gunmen used a stolen helicopter and explosives to engineer a spectacular raid on a cash depot in Stockholm yesterday, breaking into the building through the roof and flying off with bags of cash, police said.

The daring pre-dawn heist stunned police, who could not deploy their own helicopters to the scene because explosives had been placed at their hangar.

Investigators believe at least 10 professional criminals were involved. "These are people who most likely have committed similar crimes before," the police spokesman Ulf Goranzon said. "We have naturally activated police throughout Sweden as much as possible. Especially when it comes to border controls."

The security company that owns the facility, British-based G4S PLC, would not confirm how much money had been taken but said it would offer a large reward for information leading to the arrest of the assailants and the return of the cash.

A man was detained in a Stockholm suburb in connection with the robbery but police stressed it wasn't clear if or how he was involved. "He's suspected of handling stolen goods," Mr Goranzon said. "We'll have to see if he has anything to do with this."

Shortly after 5am, the masked robbers dropped on to the roof of the cash depot from a helicopter, Mr Goranzon said. They entered through a window and explosions were heard as they travelled through the building to access the areas where money is kept.

"What we know is that they forced down some kind of wall to get in," another police spokesman, Christian Agdur, said. "We don't want to comment on how they did it."

There were 21 workers inside the building but no one was injured. Investigators said that the robbers wore masks, were believed to have been carrying weapons and used explosives during the 20-minute raid. Witnesses reported hearing loud bangs.

Bjorn Lockstrom told the broadcaster TV4 that he saw a helicopter hovering above the building for about 15 minutes. "Two men hoisted themselves down. I saw when they hoisted up money, too."

A police commando team was seen trying to enter the building in the Vastberga neighbourhood with a battering ram. Police later found an abandoned helicopter near a lake north of Stockholm, about 15 miles (25km) from the cash depot. The police spokeswoman Towe Hagg said the chopper was reported stolen and was believed to be the one used by the robbers.

A bomb squad examined a suspected bomb left at the police hangar, which prevented their helicopter from taking off. It was found to be live.

G4S PLC is one of the world's largest security companies. Its depot stores cash that is transported to banks and businesses in Sweden.

Last year, a group of men broke into a mail processing centre in Goteborg in Sweden, paralysing large parts of the city after spreading out spikes, burning out cars and leaving suspected explosive devices in the centre.

In 2006, Goteborg's international airport was partially closed after men crashed through a gate and held up luggage handlers who were unloading crates of currency worth 7.8 million kronor (£695,000) from an aircraft.

Four years earlier, robbers pulled off a similar heist at Stockholm's Arlanda Airport, when staff were loading foreign currency worth 43 million kronor on to an aircraft.