(CNN) - The trial has begun in Berlin of four men accused of stealing a huge, commemorative gold coin worth an estimated €3.75 million ($4.31 million) in an old-school heist.
"Big Maple Leaf," which has a diameter of 21 inches, is thought to be the second-largest gold coin in the world, according to the AFP news agency.
The coin, which features a portrait of the UK's Queen Elizabeth II, was minted in 2007 by the Royal Canadian Mint.
At the time of the theft on March 27, 2017, the coin was part of an exhibition at the Berlin Bode Museum. The defendants broke in through a window, press spokeswoman Lisa Jani of the Berlin Regional Court, where the trial is taking place, told CNN.
Three co-defendants, Wissam R., Ahmed R. and Wayci R., are accused of breaking in using information passed on by another defendant, Dennis W., a former security guard at the museum, said Jani.
The thieves escaped with the 220-pound (100-kilo) coin through the broken window then hauled it over some nearby railway tracks, according to court documents.
Three of the defendants are part of the Remmo clan, one of a number of well-known crime families in Germany that experts say formed there following the arrival of Lebanese and Palestinian migrants from the late 1970s onwards.
Last summer, German authorities seized 77 properties worth 10 million euros ($11.5 million) owned by the Remmo clan, said Ralph Ghadban, author of the book Arabic Clans and an expert on the subject, in an interview with CNN.
"These are no trifles," he said, adding that the Remmo clan controls at least two districts in Berlin and continues to expand its operations.
Although the thieves escaped at the time, they were arrested in July 2017 as part of a Berlin police operation detailed by the force on Twitter.
Despite executing 14 search warrants police have been unable to find the coin, and Ghadban told CNN that its disappearance is a boon for the Remmo clan.
"It still hasn't been found until today and will probably never be found," he said. "That brings a lot of prestige and power on the street because they control certain areas for their blackmailing and protection activities. When you have more respect (this) can bring more power to the areas under the influence."
The trial is taking place in a youth court because the defendants were adolescents, aged 18-21 under German law, at the time of the crime.
The defendants could face up to 10 years in prison.
The Bode Museum says it "presents a history of humankind in metal," with coins and medals as well as other forms of money in a collection of more than half a million objects.