A prosecutor says the Easter weekend heist in London's Hatton Garden diamond district was the largest burglary in English legal history.

The haul was worth an estimated 14 million pounds ($21 million).

Prosecutors said Monday the thieves used "sophisticated" methods and meticulous planning to drill into the wall of a vault in the jewelry district before ransacking 73 safe-deposit boxes.

Four men said to be ringleaders have already pleaded guilty to conspiracy to commit burglary.

Four others are on trial at Woolwich Crown Court accused of involvement in the high-profile theft, which generated wide coverage in Britain.