A British auctioneer who was at the centre of a BBC investigation has pleaded guilty at a New York court to a series of charges in connection with unlawful sales of rare ancient coins.

Richard Beale, director of London-based auction house Roma Numismatics, admitted two counts of conspiracy and three counts of criminal possession of stolen property, court documents show.

He was accused of falsifying the provenance of the most expensive coin ever auctioned – the gold Eid Mar, which fetched $4.19m (£3.29m) in 2020 – and an ancient silver Sicily Naxos Coin, which sold at the same time for $292,000.

He has also admitted to falsifying the provenance of a number of silver Alexander the Great decadrachms from the “Gaza Hoard”, which were sold by Roma Numismatics and whose suspicious origin was brought to light by a BBC News Arabic documentary in 2020.

The investigation documented how, three years earlier, fishermen in the Palestinian territory had discovered dozens of the coins, which date back to the 4th Century BC. Soon after the coins were found, they disappeared.

“They are in the hands of people who don’t know what these [coins] are, why they are here and what they represent for our country. It’s very painful,” Fadel Alatol, a local archaeologist who had identified the coins found by the fishermen before they were presumably sold on, told the BBC in 2019.

Before the Gaza discovery, only 20 Alexander decadrachms were known to be in existence. A few months later, the same type of coins started to appear for sale at auction houses around the world.

In September 2017, one Alexander decadrachm sold for £100,000 ($127,300) at Roma Numismatics.

But in total 19 of these, formerly very rare, Alexander decadrachms were sold – 11 of them by Roma Numismatics – with the provenance of the coins listed as either “from a private Canadian collection” or “ex-private European collection”.

In 2019, the BBC approached Beale at his office in London and challenged him directly about the provenances for the decadrachms listed on Roma Numismatics’ auction site.

The BBC informed Beale that it suspected the coins had come from the “Gaza Hoard”, which meant that it was illegal to sell them.

Auction houses are expected to carry out due diligence to establish a coin’s provenance. However, they are also permitted to rely only on what they are told by a trusted consignor – the technical term for a sender.

In a statement provided to the BBC by Beale at the time, he said: “We were satisfied that the consignor(s) were known to us, and had an established record of professionalism and trust. Furthermore, we were provided with information that the items had entered the UK from an origin country that raised no concern.”

Following the meeting with BBC producers, Roma Numismatics went on to sell more Alexander decadrachms.

Appearing before the New York Supreme Criminal Court on 14 August, Beale admitted that he had known the provenances of the decadrachms were false when they were sold and meant to disguise the fact that they came from the Gaza Hoard, court documents show.

He also admitted that he decided to continue selling the coins despite the producers of the BBC documentary challenging directly about the false provenances on Roma Numismatics’ auction site.

According to the court documents, Beale also admitted that in 2015 he entered into an agreement with an Italian coin dealer to sell the Eid Mar coin, which was minted in 42BC to commemorate the assassination of Julius Caesar on the Ides of March.

The two men travelled to Munich and paid €450,000 ($490,000; £385,000) in cash for the coin, despite it having no provenance paperwork or any other form of documentation.

In August 2020, Beale shipped the coin to the US to be authenticated and listed its country of origin as “Turkey”, because any ancient items from Italy or Greece were more likely to be seized by US Customs for checks.

The following month, the coin was listed for sale by Roma Numismatics and described as coming “from the collection of the Baron Dominique de Chambrier, original attestation of provenance included”.

In October 2020, Beale received an email and letter from the baron asking him to withdraw the false provenance. But he proceeded with the sale of the coin and an American buyer paid $4.19m.

Judge Althea Drysdale called Beale’s actions “woefully wrong and illegal”, as well as “harmful to both the buyers and the nations whose cultural property [was] illegally acquired”.

The maximum sentence for these criminal offences is 25 years in prison, but this could be reduced under a plea and sentence agreement with prosecutors.

Beale is next due to appear before the New York Supreme Criminal Court in March.

Both the Eid Mar and Sicily Naxos coins were seized by US authorities and repatriated earlier this year to their countries of origin – Greece and Italy.