A federal jury in Pennsylvania began hearing a tale Thursday that has long fascinated coin collectors: how a Philadelphia family ended up with a stash of exquisitely rare $20 gold coins from 1933 that the U.S. Mint never circulated.

The 10 coins could bring $80 million or more at auction. But it's not clear that day will ever come.

Federal attorneys told the jury in opening statements that the coins belong to the United States because they were never legally released by the U.S. Mint in the 1930s.

But descendants of the late Philadelphia jeweler Israel Switt say the government can't prove they were stolen. Switt, who dealt in scrap gold, might have legally traded for them in his regular dealings with the Mint, their lawyers said.

U.S. District Judge Legrome Davis promised jurors selected for the trial that the case would be more fascinating than anything they see on TV, a case replete with history about the gold standard, the Depression, and decades of sleuthing over the rare 1933 Saint-Gaudens "double eagles." The trial is expected to last two to three weeks.

"The government must prove that these coins were stolen three-quarters of a century ago," lawyer Barry Berke, who represents Switt's daughter and grandsons, told the jury.