A group of burglars pulled off the biggest heist in British history.

Hatten Garden, part of London’s most exclusive jewelry district, was hit for up to 200 million euros in jewels and cash. The gang is thought to already be out of the country. The break in happened April 9 at night, after the security had left the building. It is thought that the group broke into the offices above Hatten Garden and cut through the roof before going down the lift shaft.

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Image: http://www.mirror.co.uk/news/uk-news/hatton-garden-jewellery-robbery-stolen-5480357

The former head of the Flying Squad, a law enforcement task force in charge armed robberies in London, says the thieves already sent their items somewhere out of the country as well.

“It was a highly organized, sophisticated crime. It’s highly likely that any gems or jewelry will have already been sourced and out of the country,” he said. An alarm sounded at 1 p.m. on Friday, but the premises was not fully checked. Detectives are investigating if the gang had Hatten Garden under surveillance by the criminals in the weeks leading up to the heist. The most valuable item stolen was a half-cut aqua diamond worth 500,000 Euros.

Upset customers have gathered outside of the store, in shock that many of the deposit boxes were left unsecured.

“I can’t believe this has actually happened,” Michael Miller, a London jeweller said. “If you look at their website, they say they are the safest place around. There is a double-door entry and a locked system to go in. You have to go through two doors to get in the place and then get into the vault.”

Experts say it is almost impossible that the gang did not have access to some kind of inside knowledge about the building’s layout and security. They cut through 2 walls of metal security bars before disabling the alarm on the vault’s main door.