The young woman in question is depicted sitting on the floor topless in a painting by the impressionist Henri Matisse, “Odalisque in Red Pants,” which was stolen from a museum in Caracas more than a decade ago.

On Tuesday, F.B.I. agents in Miami arrested two people in a sting operation and accused them of trying to sell the long-lost painting, said to be worth $3 million. The news caused a stir in Caracas, where the young woman’s strange disappearance had left a hole in the art world.

The theft of the painting was first discovered in late 2002, when the Contemporary Art Museum of Caracas was contacted by a Miami gallery owner saying that someone had offered to sell it to him. Experts at the museum inspected the likeness and were shocked to find that it was a fake, and not a very good one, at that.

Someone had removed the original painting from its frame and put the fake in its place, leaving it to be exhibited as if it were the real thing. And no one noticed.

The fake painting appears to have been hanging in the museum for at least two years and perhaps longer.

Marianela Balbi, a journalist who wrote a book about the theft, said that a photograph taken in September 2000 shows President Hugo Chávez standing in the museum in front of the fake Matisse. That is the earliest indication of the switch, she said.

The next month the museum heard from a Matisse expert that someone was shopping the painting around, Ms. Balbi said. But it appears no one followed up, and the theft went undiscovered for an additional two years.

Mr. Balbi said that the Caracas police had no experience with this type of art theft and the investigation went nowhere. The trail then went cold until a few months ago.

According to an affidavit filed in federal court in Miami, the F.B.I. learned last year that a Miami man named Pedro Antonio Marcuello was trying to sell the painting. Agents posing as buyers began negotiating with Mr. Marcuello, ultimately agreeing to buy the stolen artwork for $740,000.

This week, a woman named María Martha Ornelas flew to Miami from Mexico City, carrying the painting rolled up in a red tube. She and Mr. Marcuello met with the agents at a hotel, where the agents inspected the painting and then arrested the two.

According to court papers, Ms. Ornelas told F.B.I. agents before her arrest that the painting had been stolen by museum employees, who had replaced it with the fake. She said, without disclosing details, that the painting had been in her possession for years.

The Matisse was not the only artwork to have disappeared from the museum. Rita Salvestrini, a former director, said that a 2001 inventory identified 14 missing pieces, although it did not detect the Matisse forgery. She said most of the missing works had never been located.

At the scene of the original crime, the museum was all but deserted on Thursday afternoon. Only a couple of visitors passed through the subterranean Gallery 9, where the Matisse had once been exhibited.

Upstairs, Rafael Perreira, a professor of art history of the Central University of Venezuela, said that under Mr. Chávez’s government, museums had been neglected and underfunded.

“There has been a demonization of culture,” he said, adding that Mr. Chávez’s socialist government equated art like the Matisse with bourgeois values.

“She left a country where people knew her worth,” Mr. Perreira said of the woman in the red pants. “She will come back to a country where she means nothing.”