POTSDAM, Germany (AP) _ It was early in World War II and the legendary Amber Room, looted from a Russian palace, was being shipped back to German territory. When the convoy came under fire, a German soldier took advantage of the confusion to purloin a piece for himself.

Now the gold-framed mosaic of marble and semi-precious stones may be the only part of the 18th century treasure to have survived.

German officials this week confiscated the mosaic, depicting two couples lounging in a garden with their dogs, from a Bremen lawyer who said he was selling it on behalf of the soldier's son.

Police said at a news conference Thursday they believe the mosaic is the real thing, although additional tests are still being conducted.

But because it apparently was swiped by the soldier in 1941, its recovery brought police no closer to solving the mystery of the Amber Room's disappearance in early 1945 from the German city of Koenigsberg, now the Russian port of Kaliningrad.

German officials were reluctant to comment on whether the 22-by-28-inch artwork would be returned to Russia.

``That depends on a lot of things,'' was all Chief Prosecutor Ruediger Schmidt would say when asked at a news conference. A German Foreign Ministry spokesman said no decision would be made until after the final tests determine its authenticity.

The issue of trophy art has been a sore point in German-Russian relations since the end of World War II. Both sides looted museums, libraries, castles and churches as their troops advanced, and the Amber Room is high on Russia's list of 40,000 art objects it wants back from Germany.

The ornate, 1,300-square-foot hall was a gift of Prussian King Friedrich Wilhelm I to Russia's Peter the Great. The wall panels were made from golden brown amber, with four mosaics representing the human senses.

The room was installed in a palace Peter built for his wife, Catherine I, outside of St. Petersburg.

Nazi troops dismantled it when they captured the village and shipped it to Koenigsberg, where it was installed in a castle. But it disappeared in 1945 as the Red Army moved west, and years of searching have turned up no trace.

German officials learned the mosaic was being offered for $2.5 million this year while investigating the theft of a painting.

At a meeting in a Berlin restaurant in January, undercover police were offered the stolen painting, a Hitler self-portrait and the Amber Room mosaic, said Potsdam police chief Peter Schultheiss.

With the help of a middle-man and money put up by a German newsmagazine, Schultheiss, using his own name but posing as a representative of a big company, let his interest be known.

He was given a videotape of the mosaic and later samples of the wooden frame and resin used to hold the tiles, all of which were examined by experts who concluded it could be authentic.

Last Sunday, the offer came to examine the mosaic in person. The meeting was held above a shop in Bremen, with police stationed outside.

Lawyer Manhard Kaiser told police the soldier, a Wehrmacht truck driver, took the mosaic in 1941 when the transport came under fire. It hung for years over the sofa in his apartment, then after his death in 1978, the man's son stored it in the basement because he didn't like it.

Only after seeing a TV report a few years ago on the Amber Room did the son realize what he had and decide to sell it, according to Kaiser, who refused to identify his client.