At first, nothing seemed out of place when Michael Bakwin returned to his home in the Berkshires after he and his family went away for Memorial Day weekend in 1978.

But the next day, Bakwin's wife walked into the dining room and saw that seven paintings had been stripped from the walls, including a still life by the French impressionist Paul Cezanne now worth tens of millions of dollars. The theft set off an international investigation that led to Monaco, Geneva, London and — finally — to a retired lawyer.

Robert Mardirosian, 73, of Falmouth, went to trial Tuesday on federal charges of possessing and transporting stolen goods. He's accused of trying to sell the paintings, which had been stolen by one of his clients.

Prosecutor Jonathan Mitchell told the jury that Mardirosian knew the paintings were stolen and repeatedly tried to make money on them over 30 years, at first by trying to collect a reward or insurance money, and later by negotiating a deal to return the most valuable painting — Cezanne's "Bouilloire et Fruits" — in exchange for Bakwin turning over title to the other six paintings.

"Instead of returning those paintings, he decided to keep them. He wanted to cash in on them," Mitchell said.

Mardirosian's attorney, Brian Fitzsimmons, told the jury his client was simply trying to return the paintings to their rightful owner and collect a finder's fee.

"He took the view that a finder's fee was the usual and standard practice," Fitzsimmons said.

Bakwin testified that his parents had given him most of the paintings — including the Cezanne — in the 1950s and 1960s. He described seeing the empty walls in his dining room and the frame to the Cezanne painting on the floor.

"I sort of went into shock," he said. "I loved those paintings for all those years, and they were gone."

Mitchell told the jury that Mardirosian knew the paintings were stolen shortly after the theft in 1978, when David Colvin, a client he was representing on an unrelated firearms charge, carried the artwork to his office in a plastic bag. A year later, Colvin was murdered over a gambling debt.

Bakwin said he offered a $25,000 reward for several months after the theft and hired a private detective to try to find the paintings. He said he heard nothing for more than 20 years.

Meanwhile, Mardirosian moved the paintings to Monaco in 1988 and later to a bank in Geneva. He said he planned to return them to Bakwin for a finder's fee of 10 percent of their value, prosecutors said.

In 1999, Bakwin said he received a call from The Art Loss Register, a London-based organization that keeps a database of lost and stolen artwork. Lloyd's of London had been contacted by someone who inquired about insuring the paintings before sale.

Bakwin said he signed a contract with the Art Loss Register to try to find out who had the paintings.

Prosecutors said Julian Radcliffe, chairman of the register, determined that the paintings were being sold by a Panamanian corporation called Erie International Trading Co., which was later found to be registered to Mardirosian.

Bakwin said Radcliffe brokered a deal with agents of Erie, who agreed to return the Cezanne in exchange for the other six paintings. Two months after getting the Cezanne back, Bakwin said he sold it for $29.3 million through an auction by Sotheby's of London.

Bakwin said he considered the deal "extortion" and never turned over the titles to the other six paintings.

In 2005, Mardiorisian tried to sell four of the paintings through Sotheby's, but Bakwin stopped the auction by suing in a London court, Mitchell said. Mardiorisian was arrested in February 2007.