A woman has been accused of posing as a jewel expert to snatch diamonds worth £4.2 million (US$5.7 million) from a luxury London jeweler, swapping them for garden pebbles in a highly sophisticated "sleight of hand" heist in 2016, a court has heard on Tuesday.

The suspect, Lulu Lakatos, 60, who was born in Romania but lived in France, has been charged with conspiracy to steal diamonds from a Boodles store in central London, along with five others. The woman, however, maintains her innocence and denies any wrongdoing. 

Prosecutors allege that in February 2016, Boodles chairman Nicholas Wainwright, 73, was introduced to an Israeli man who identified himself to be “Simon Glas.” The man then claimed to be interested in buying high-value diamonds as an investment with purported Russian business partner “Alexander,” the New York Daily News reported.

It follows a meeting in a Monaco hotel, which secured the deal for the purchase of the seven diamonds. Lakatos, who posed as the group's gemologist named "Anna," was then sent to the jewelry shop in London's Mayfair area on March 10, 2016, to value seven diamonds on behalf of a group of wealthy Russian buyers.

The court heard that the suspect moved to examine and weigh the diamonds before securing them inside opaque boxes placed into a zippable purse-like bag which was padlocked shut.

According to Boodles’ in-house gemologist Emma Barton, Lakatos then placed the locked purse inside her handbag when the owner went upstairs to take a phone call from Glas. 

Barton called the woman out and told her to put the bag back on the table, which the suspect did, successfully swapping the looted item for an identical locked purse, 9News noted.

The following day, Boodles arranged for the bag to be X-rayed and confirmed diamond-like stones were inside. However, the purse was unlocked following growing suspicions from the staff. 

They found out that each of the opaque boxes contained a small pebble instead of the gems, which included a 20-carat heart-shaped diamond and a three-carat pear-shaped fancy pink diamond worth a total of £4.2m (US$5.7 million).

“The diamonds had been stolen by the defendant by sleight of hand,” prosecutor Philip Stott said. “The conspiracy in which she is alleged to have played an integral and central part was one of the highest possible sophistication, planning, risk, and reward.”

Just three hours after the reported theft in 2016, all six schemers were already out of the U.K. Lakatos was only arrested in France on a European arrest warrant in September last year before being extradited to the U.K.

Meanwhile, two of the group members, Christophe Stankovic and Mickael Jovanovic, have already been convicted of conspiracy to steal, according to the Guardian.

diamonds Boodles found out that each of the opaque boxes contained a small pebble instead of the gems, which include a 20-carat heart-shaped diamond and a three-carat pear-shaped fancy pink diamond worth a total of £4.2m (US$5.7 million). This is a representational image. UNSPLASH